long claws, and their blades placed something like the arms of a Maltese cross, whence their name; 6 stamens, 4 of which are longer than the other 2; and a fruit consisting of 2 cells, with a central frame, to which is fitted a pair of deciduous valves, and from the sides of which under the valves is stretched a thin double transparent diaphragm. In each cell are two or more seeds, with an embryo folded upon itself, and destitute of albumen. The form of the fruit is extremely variable: when it is long and slender it is called a Silique, and when short and round a Silicle; hence the two divisions of the Tetradynamia of Linnæus into Siliquose and Siliculosa.

About a couple of thousand species are dispersed over the milder parts of the world, refusing alike to exist beneath the severe cold of the arctic zone and the excessive heats of the tropics. A large proportion consists of inconspicuous and useless weeds; many are objects of beauty from the size and gay colours of their petals; and the names already mentioned show that another part of the order consists of plants useful to man.

will be the same embryo with the radicle applied to the back of the cotyledons; and B 2 and C 2 will give the section and sign of what are called Notorhizea. When the cotyledons instead of being flat are channeled so as to receive the radicle in a kind of groove, as at A 3, it gives the division Orthoploceæ. If the cotyledons are so long as to be doubled twice, A 4, they constitute Spirolobea; and if, as at A 5, the cotyledons are doubled three times, they indicate the division Diplecolobec. Upon these distinctions all recent arrangements of Crucifera have been formed.

The affinities of this order are with Papaveracea, Cistaceae, Capparidaceae, and Fumariacea. There are 173 genera and above 1600 species described. It is eminently a European order: 166 species are found in Northern and Middle Europe, and 178 on the northern shore or islands of the Mediterranean; 45 are peculiar to the coast of Africa between Mogadore and Alexandria; 184 to Syria, Asia Minor, Tauria, and Persia; 99 to Siberia; 35 to China, Japan, or India; 76 to Australia and the South Sea Islands; 6 to Mauritius, and the neighbouring islands; 70 to the Cape of Good Hope; 9 to the Canaries or Madeira; 2 to St. Helena; 2 to the West Indies; 41 to South America; 48 to North America; 5 to the islands between North America and Kamtchatka; and 35 are common to various parts of the world. This being their general geographical distribution, it appears that, exclusive of the species that are uncertain or common to several different countries, about 100 are found in the southern hemisphere and about 800 in the northern hemisphere; or 91 in the New and the rest in the Old World. Finally, if we consider them with regard to temperature, we shall find that there areIn the frigid zone of the northern hemisphere

In all the tropics (and chiefly in mountainous regions)
In the temperate zone-

Of the northern hemisphere

205

30

548

Of the southern hemisphere 86 634 Such were the calculations of De Candolle in 1821. Although requiring considerable modification, especially in the Asiatic and North American numbers, which are much too low, they serve to give a general idea of the manner in which this order is dispersed over the globe.

The character of the genera of this order is antiscorbutic and stimulant, combined with an acrid flavour. The officinal species are among the commonest of all plants, and will be found treated of under their respective heads. A large number of genera are natives of Britain. The following is a synopsis of the British genera, according to Babington's 'Manual of British Botany:'

Cheiranthus Cheiri.

1, a flower from which the petals have been removed; 2, the stamens; 3, a section of the ovary; 4, a ripe fruit, from which the valves are separating; 5, an embryo.

Owing to the number of the species, and the great resemblance between them, the systematic arrangement of Cruciferous Plants was until late years exceedingly unsatisfactory. It has however been discovered that the embryo presents the most constant character, and that by five modifications of the manner in which it is folded up five precisely limited divisions of the order are secured. The following cut illustrates them. Let A 1 be an embryo with the radicle applied to the cotyledons in such a way as to lie against its edges; then B 1

7. Cardamine.

8. Dentaria.

Tribe II. SISYMBRIEÆ.

Cotyledons incumbent, contrary to the dissepiment; radicle dorsal seed compressed.

9. Hesperis.

10. Sisymbrium.
11. Alliaria.

12. Erysimum. Tribe III. BRASSICE.

Cotyledons conduplicate, longitudinally folded in the middle; radicle dorsal within the fold.

13. Brassica. 14. Sinapis. 15. Diplotaxis. Sub-Order II.

LATISEPTE.

Pouch (silicle) short, opening with two valves; dissepiment in its broadest diameter.

Tribe IV. ALYSSINEE.

Cotyledons accumbent.

16. Alyssum. 17. Koniga. 18. Draba.

19. Cochlearia.

20. Armoracia. Tribe V. CAMELINEE.

Cotyledons incumbent.

Tribe IX. SUBULARIEÆ.

forms, as among animals higher in the scale, a kind of inorganic lamina, applied to the surface of the corium, from which it is an exudation. After the fall of the old shell it becomes thicker and very considerably firmer, owing to the deposition or penetration of calcareous molecules within its substance, as well as by the addition of new layers to its inner surface. The degree of hardness finally acquired, however, and the amount of calcareous matter deposited within it, vary considerably; in many members of the class, it remains semicorneous, in a condition very similar to that of the integuments of insects, with which, moreover, it corresponds very closely in point of chemical composition; in the higher crustaceans, again, its composition is very different: thus, whilst chitine in combination with albumen is the principal element in the tegumentary skeleton of some species, this substance scarcely occurs in the proportion of one or two tenths in the carapace of the Decapods, which, on the contrary, contains 60 and even 80 per cent. of phosphate and carbonate of lime, the latter substance particularly occurring in considerably larger

29. Subularia.

less a membrane or reticulation than an amorphous matter diffused through the outermost layer of the superficial membrane, being secreted like this by the corium. Alcohol, ether, the acids, and water at 212° Fahr., change it to a red in the greater number of species; of these different agents without undergoing any perceptible change. The epidermic layer hardened in different degrees is the part which mainly constitutes the tegumentary skeleton of the Crustacea. In its nature it is obviously altogether different from that of the internal

30. Senebriera.

Sub-Order IV. NUCAMENTACEÆ.

Tribe XI. ISATIS.

Cotyledons incumbent.

31. Isatis.

Sub-Order V. LOMENTACEE.

physiological resemblance has led naturalists to speak of these two pieces of organic mechanism, so dissimilar in their anatomical relations, under the common name of skeleton. The tegumentary skeleton of the Crustacea consists, like the bony skeleton of the Vertebrata, of a great number of distinct pieces connected together by means of portions of the epidermic envelope which have not become hardened,

CRUCIROSTRA. [LOXIADE.] CRUSTA CEA, Crustacés of the French, Krustenthiere of the Germans, Malakósтрака of Aristotle and the ancient Greeks, a class of Articulated Animals, whose external covering is less solid than that of the majority of Testaceous Mollusks, but much firmer and harder than the skin of the Naked Mollusks; and whose conformation is essentially distinguishable from other classes, especially in the circulating, respiratory, and locomotive organs. The Common Crab [CRAB], the Lobster, and Crayfish [ASTACUS], the Common Shrimp [CRANGONIDE], and the Water-Fleas [BRANCHIOFODA], may be taken as types of different sections of this family.

As in many of the Testaceous Mollusks, the skeleton of the Crustacea is external. It is made up of the tegumentary envelope, which, in some of the class, always continues soft, but in the greater portion is very firm, forming a shelly case or armour, in which all the soft parts are contained. In the more perfect Crustaceans it is complex. The following description of its component parts is from the pen of M. Milne-Edwards, who, in his Histoire Naturelle des Crustacés' (Paris, 1834, &c., 8vo), and in the article 'Crustacea' in the Cyclopaedia of Anatomy and Physiology (London, 1836, &c.), has given the most complete view of the organisation of this family. Taking the Brachyura, or Short-Tailed Crustaceans, as his instance of the more highly developed forms of the class in which the complex structure is exhibited, he thus proceeds, "The integument consists of a corium and an epidermis, with a pigmentary matter of a peculiar nature, destined to communicate to the latter membrane the various colours with which it is ornamented. The corium or dermis, as among the Vertebrata, is a thick, spongy, and very vascular membrane; on its inner surface it is intimately connected with a kind of serous membrane, which lines the parietes of the cavities in the Crustacea in the same manner as the serous membranes line the internal cavities among the Vertebrata; these two membranes, divided in the latter order by the interposition of muscular and bony layers, which cover and protect the great cavities, become closely united when these layers disappear, as they do in the Crustacea, in consequence of the important changes that take place in the conformation of the apparatus of locomotion. The corium again, among the Crustacea, is completely covered on its outer surface by a membranous envelope unfurnished with blood-vessels, and which must be held in all respects as analogous to the epidermis of the higher animals. It is never found in the properly membranous state, save at the time of the Crustacea casting their shell; at this period, it is interposed between the corium and the solid covering ready to be cast off, and has the appearance of a pretty dense and consistent membrane, in spite of its thinness. It

connected by cartilages, the ossification of which is only accomplished in extreme old age.'

This skeleton, or crustaceous frame-work, consists of a series of rings varying in number, the normal number of the body-segments being twenty-one. Instances of a larger number are rare, and a less number seldom occurs; one or more rings may be apparently absent, but in such cases they will generally be found consolidated as it were. In the embryo the segments are developed in succession from before backwards; the posterior rings therefore are generally absent when the number is defective. Each ring is divisible into two arcs, one upper or dorsal, the other lower or ventral. Each arc may present as many as four elementary pieces. Two of these united in the mesial line form the tergum; the sides of this upper arc are framed of two other portions denominated flanks or epimeral pieces. The lower arc is a counterpart of the upper. Two of the four pieces into which it is divisible constitute the sternum, situated in the mesial line, and are flanked by two episternums. These two arcs do not cohere at their edges, but a space is left for the insertion of the lateral appendages or extremities which correspond with them. (Milne-Edwards; Audouin.)

The one-and-twenty rings above mentioned are generally divisible into three sections of seven each, and may be considered as corresponding with the three regions which zoologists have generally consented to recognise in the bodies of the crustaceans, under the denominations of a head, a thorax, and an abdomen; but the student should be on his guard against the false impressions which, as M. MilneEdwards observes, are likely to arise from these terms, by their leading the mind to liken them to the grand divisions in the Vertebrata, which are defined by the same expressions.

The cephalo-thoracic portion and carapace first claim our attention, and the latter acquires its greatest development in the Decapods. "In these animals," says M. Milne-Edwards, "the frame-work of the body does not appear at first sight to consist of more than two portions, the one anterior, formed by the carapace, and representing the cephalic and thoracic segments conjoined; the other posterior formed by the abdomen. In reality, the first fourteen rings of the body are covered by this enormous buckler, and are so intimately conjoined as to have lost all their mobility; the whole of the thoracic segments thus hidden below the carapace are connected with it in their superior parts; they are only joined with one another underneath and laterally; and their tergal parts having, in consequence of this, become useless, are no longer to be found, being in some sort replaced by the great cephalic buckler; thus the whole of these rings, in conformity with this arrangement, are imperfect and open above."

The subjoined cut represents the carapace of a Brachyurous or Short-Tailed Crustacean, and the regions of which it is composed, named after the viscera and organs protected by them.

The succeeding figure represents the carapace of a Macrourous or Long-Tailed Crustacean.

The abdomen is most fully developed in the Macroura, or Long-Tailed Crustaceans, in many of which it becomes a very important organ of motion, and in them there is a comparatively small development of the carapace; while in the Brachyura, or Short-Tailed Crustaceans,

View of the under side of the male of Thelphusa fluviatilis, with the male organs. The detached figure represents one of these organs.

On this subject Professor Bell remarks:-" When we consider the almost endless diversity of form under which the species composing this class of animals appear, the astonishing discrepancy which exists in the forms and relative proportions of the different regions of the body, and other parts of their organisation for the performance of offices and functions equally various, and see that all these diversities are produced only by modifications of a typical number of parts, we cannot but be struck by so remarkable and interesting an illustration of the great economical law, as it may be termed, that the typical structure of any group being given, the different habits of its component species or minor groups are provided for, not by the creation of new organs or the destruction of others, but by the modification in form, structure, or place, of organs typically belonging to the group."

One of the necessary consequences of the condition of these animals inclosed in a hard shell is the power they possess of throwing it off. If this were not the case all growth would be stopped, excepting increase of thickness in the shell by a succession of secretions from below. To allow therefore room for the expansion and growth of the body and limbs, a provision for their increase is made by means of moulting, which, as a general rule, is more frequent the younger the animal is, as indeed might be expected. Thus eight moults in the short space of seventeen days have been observed in a young Daphnia. [BRANCHIOPODA.] It can be easily observed in the Common Crab. [CANCER.]

In Astacus fluviatilis, the moult, or Ecdysis, as this process is called, is preceded by a few days of fasting and sickness, and at that time the carapace becomes loosened from the corium to which it was attached. The corium begins forthwith to secrete a new shell, which is at first soft and membranous, becomes gradually harder and harder, and is at last calcareous. When all connection with the old shell is broken off, and the corium has completely secreted the new mem

this rule is reversed, the abdomen being comparatively small, and the great development taking place in the carapace, illustrating the "loi de balancement organique" of M. Geoffroy St. Hilaire. The Common Crab and Common Lobster afford striking examples of this law of organic equivalents.

m

View of the under side of the female of Thelphusa fluviatilis, with the tail or abdomen extended.

a, b, c, d, e, sternal pieces; f, g, h, i, latero-sternal pieces; k, k, external apertures of the female organs of generation; 1, 1, 1, abdominal appendages, or false feet. The detached figure represents one of these appendages removed from the abdomen; the palp marked m carries the ova during incubation.

the old incumbrance, and becomes very restless, the symptoms of draws nigh. It rubs its legs one against the other, and finally throws inquietude increasing in proportion as the time for emancipation itself on its back. In that situation it begins to shake itself and swell itself out, till it tears the membrane which connects the carapace with the abdomen, and begins to raise the former: then it rests a while. Alternations of agitation and rest succeed each other at intervals of longer or shorter duration, the carapace is completely raised, the head, the eyes, the antennæ, are extricated. The greatest difficulty occurs in freeing the extremities, nor could they be extricated at all did not the old covering split longitudinally and indeed it frequently happens that the Crawfish leaves a limb or two behind; and is sometimes so fettered, that it perishes from inability to extricate itself. The abdomen is the last division of the body freed, and the whole change generally takes place in half an hour. Four-andtwenty-hours, or two or three days at furthest, are necessary for the conversion of the soft and membranous integument which sheathes the corium or naked body into a firm calcareous case similar to the last, and presenting the same appendages, even to the hairs; although M. Milne-Edwards has stated that these last organs are not formed within the old ones, as supposed by Réaumur, but exist ready-formed in the new envelope, turned in towards the interior like the fingers of a glove turned in upon itself.

Mr. Spence Bate of Plymouth, who has very successfully studied the Crustacea, states that he has confirmed the original observation of Réaumur.

M. Milne-Edwards observes that the time occupied in the business of throwing off the shell varies considerably in different species, and that it also depends on atmospheric influences; and this observation applies equally to the number of days required for giving the new tegumentary sheath the consistency of the old shell; and he adds, that in the whole of the species which have been duly watched, especially those found on the French shores, the period which precedes and that which follows the Ecdysis is a period of inquietude and disorder. The muscles are then flaccid, the flesh is soft and watery, and the animals are considered unwholesome and unfit for food. An

exception to this remark occurs in the Land-Crabs (Gecarcinus), which, according to the testimony of all who have spoken and written on the subject, are never so delicious as during the season of change.

At the period of Ecdysis, rounded flattened calcareous concretions (carbonate of lime), commonly called Oculi Cancrorum, are formed at the sides of the stomach of the common river crawfish. (Prep. 406, Mus. Coll. of Surg.) Every one has occasionally been struck with the difference of size in the members of crabs and lobsters. One claw of these, and other crustaceans which have the claws, when perfect, nearly equal, is often found of its full volume, while the other is comparatively diminutive; for the animal, upon the limb receiving any injury, has the power of suddenly throwing it off, and the effort does not appear to be attended with pain, though it is frequently made when the system receives a severe shock. [ASTACUS.] The point at which the separation takes place is always in the second articulation, near the basis of the limb, and from the stump, which speedily cicatrises, a new claw buds forth with all the proper articulations, and with an entire though miniature resemblance to the rejected member. This new claw is formed within the old shell and lies folded up until the exuvia are shed, when it appears as a part of the new skeleton. If one of the limbs be severed in any other place than the usual point of separation the stump goes on bleeding, nor does it heal. In such cases the renovating process does not commence until the animal succeeds in separating the remains of the member at the proper point, and this it does by a violent muscular contraction. Some years ago there were some Land-Crabs (Gecarcinus) at the Garden of the Zoological Society, and the apparent ease with which they parted with their smaller legs in order to escape from any one who injudiciously took them up by those members was very remarkable. They did not seem to regard the loss at all, and ran away on the remainder of their legs as if nothing had happened. Mr. Harry Goodsir has pointed out that this power of renewing the members in the Crustacea depends on a small glandlike body seated at the base of each limb. This body consists of a great number of large nucleated cells, which are interspersed throughout a fibro-gelatinous mass. It is supplied by a vessel and a nerve. Mr. Spence Bate describes the development of the shell as follows:

"Immediately above the heart, a pulp consisting of nucleated cells, areolar tissue, (and blood vessels?), is formed, extending to the internal surface of the shell, from which it is separated by a layer of pigment which gives colour to the new formation. Towards the base, that is, immediately above the heart, the cells are uniformly large and distinct, while an areolar tissue ramifies throughout the whole. As advance is made from the base, cells of less size mix with them, which increase in number as they diminish, in diameter, until they approach the layer of pigment, immediately beneath which they adapt themselves by mutual pressure into a polygonal form. The pulp extends over the whole periphery of the crab, immediately beneath the shell; the thickness of the pulp decreases with the distance from the centre; and the larger cells become fewer in number, the mass being made of the smaller cells which become the secreting organs of the future shell, which process commences previously to and is completed after the removal of the exuviæ." ('Annals of Nat. Hist.,' vol. vii.)

Of the nature of the organs of locomotion developed by the external skeleton, Milne-Edwards has given the best account:"The kind of solid sheath formed by the tegumentary skeleton of the Crustacea, and which includes in its interior the whole of the viscera and other soft parts of these animals, is required to be so constructed as not to oppose locomotion; consequently there exist, either between the different rings of the body or the various constituent elements of the limbs, articulations destined to admit of motion to a greater or less extent between these different pieces. The structure of these articulations is of the most simple kind; the moveable piece rests upon that which precedes it by two hinge-like joints, situated at the two extremities of a line perpendicular to the plane in which the motion takes place. In the internal portion of the edge of the moveable piece comprised between the joints there exists a notch of greater or less depth, destined to admit of flexion, whilst on the opposite or external side the same edge generally glides under that of the preceding piece. This kind of articulation, whilst it is the most favourable to precision of movement and to strength, has the disadvantage of admitting motion in one plane only; therefore the whole of the rings of the body, the axis of motion being entirely parallel, cannot move save in a vertical plane; but nature has introduced a kind of corrective of this disadvantage in the structure of the limbs, by changing the directions of the articular axis, whence ensues the possibility of general motions being performed in every direction. Between the two fixed points two opposed empty spaces are observed, left by the rings severally, and destined to admit of the occurrence of motions of flexion and extension. The tegumentary membrane which fills it never becomes incrusted or calcareous, but always continues soft and flexible.

"The tegumentary skeleton supplies the apparatus of locomotion with fixed points of action as well as with the levers necessary to motion. The immediate or active organs of this apparatus are the muscles, the colour of which is white, and the structure of which presents no peculiarity worthy of notice. They are attached to the pieces which they are required to move either immediately or by the intermedium of horny or calcareous tendons, which are implanted

upon the edge of the segment to which they belong. To the fixed point they are most commonly attached immediately. Their structure is simple, and each segment in fact, as has already been said, being contrived to move in one fixed and determinate plane, the muscles which communicate motion to it can constitute no more than two systems antagonists to each other, the one acting in the sense of flexion, by which the segment moved is approximated to that which precedes it, the other in the sense of extension, by which the segment is brought into the position most remote from the centre of motion. The muscles that produce these opposite effects, as might have been concluded, are found implanted into the opposite arms of the lever upon which their energy is extended.

"The motions in flexion tend universally to bring the extremities and the different rings towards the ventral aspect of the body; it is consequently upon this aspect that the flexor muscles are inserted, and these are in general the more powerful. On the contrary, and in accordance with the nature of the motion produced, it is upon the superior or dorsal aspect of the segments that the extensor muscles are attached. In the trench the two orders of muscles generally form two distinct layers, the one superficial, the other deep; the former thin and sometimes absent, the second on the contrary very powerful wherever powerful motions are required. The muscles generally extend from the arc above to the one immediately below, passing for the most part from the anterior edge of the upper to the anterior edge of the lower segment. The extent and the direction of the flexion of which any segment is susceptible depend on the size of the interannular spaces above or below the ginglymoid joints; and as these spaces are in general of considerable magnitude on the ventral aspect, whilst the superior arcs are in contact, and can only ride one over another in a greater or less degree, it is only downwards that the body can be bent upon itself, while upwards, or in the sense of extension, it can hardly in general be brought into the horizontal line. "Thus far what has been said applies more especially to the rings of the body, but the extremities present nothing that is essentially different, either as regards the mode in which the tubular segments are articulated to one another, or as regards the mode in which the muscles are inserted. Each of these indeed having but one kind of motion, and even that very limited in its extent, nature has aided the deficiency, as has been stated, by increasing the number of articulations, by which extent of motion is conferred, and in varying the direction of the articular axes, an arrangement by which the animal obtains the ability of moving in every direction, but at the expense of power, rapidity, and precision in its motions. Each segment of a limb incloses the muscles destined to move that segment which succeeds it, unless it be too short and weak for this end, in which case the muscles themselves have their origin at some point nearer to the medium plane of the body. As a general law the muscles are observed to be more powerful in proportion as they are nearer to the centre, which is to be explained by the fact that each motion they then communicate is transmitted to a larger portion of a limb, to a lever longer in that sense in which it is disadvantageous to the power. Occasionally however the two last segments of a member are converted into a sort of hand, and in this case the penultimate segment sometimes includes a muscular mass, which may surpass in power the same system in the whole of the limb besides. Those muscles that put an extremity generally into motion are attached to the sides of the thoracic cavity, and the apodemata supply them with surfaces of insertion of great extent, and very favourably situated as regards their action. They occupy the double rank of cells formed by these laminæ, but they vary too much in their mode of arrangement to admit of our saying anything generally upon this head. The motion of translation or from place to place, the only kind upon which it seems necessary to say anything here, is effected in two modes, either by the alternate flexion and extension of the trunk, or by the play of the limbs.

"In those Crustacea which are formed essentially for swimming, the posterior part of the body is the principal agent in enabling the animal to change its place; but here the motions, instead of being lateral, are vertical; and instead of causing the creature to advance they cause it to recede: it is by bending the abdomen suddenly downwards, and bringing it immediately under the sternum, that it strikes the water, and consequently by darting backwards that the animal makes its way through the liquid. [ASTACUS.] From what has now been said it may be imagined that the Crustacea whose conformation is the best adapted for swimming have the abdomen largely developed, and this is in fact what we always observe; the Amphi poda and Decapoda Macroura are examples; whilst in the walking Crustacea, such as the Crabs, the Caprella, the Oniscus, &c., this portion of the body attains but very insignificant dimensions. In the swimming Crustacea the appendages of the penultimate segment of the abdomen also become important organs of locomotion, inasmuch as they for the most part terminate in two broad horizontal plates, which, with the last segment, also become lamelliform, constitute an extensive caudal fin arranged in the manner of a fan. We have already said that the thoracic extremities alone constitute true ambulatory limbs. When destined for swimming only, their segments are lamelliform, and the palp, as well as the stem, contributes to form the kind of oar which each of them then constitutes.

"To conclude, the stemmatous portion of the thoracic extremities, whilst it still preserves the general form which we have assigned it, is modified in some cases to serve for walking as well as swimming, or to aid the animal as an instrument for burrowing with facility, and making a cavity for shelter among the sand. Thus in the Decapods that burrow, the last segment of the tarsus assumes a lanceolated form; and in the swimming Brachyura, the same segment, especially of the last pair of extremities (Matuta, for example), appears entirely lamellar,"

Any one who will take the trouble of going over this excellent description with a common crab and lobster before him, will have a clear idea of the locomotive system in these animals.

We have only further to add, that in a great number of species one or several pairs of the thoracic extremities are modified so as to become instruments of prehension; sometimes it is the last segment of the limb which, acquiring more than usual mobility, bends in such a manner as to form a hook with the preceding segment; sometimes It is this penultimate segment which extends below or by the side of the last, so as to form a kind of immoveable finger with which it is placed in opposition. In the first instance these instruments are denominated subcheliform claws, in the second chela simply, or cheliform claws.

adapted for sucking, and in the interior of which are two slender pointed processes that act as lancets for the purpose of perforation, in lieu of the true mandibles.

The basilar articulations of the anterior thoracic extremities in many species are employed to seize, hold fast, and in a considerable degree comminute, the food; and the most perfect development of this design is manifested in the cheliform claws of the lobsters and crabs, with all their admirable modifications for powerful prehension. The mouth is a mere opening of the short oesophagus; nor is it furnished with a tongue-the organ so named (langue and languette) is no more than a horny and lamellar process, performing in a degree the functions of a lower lip. The oesophagus, which terminates without any interruption in the stomach, and both parts, with one striking exception in the case of the latter, which we shall presently mention, present nothing remarkable, consisting, as well as the whole of the intestinal canal, of two membranous layers, and presenting a considerable resemblance to the same part of the organisation of the higher animals. The stomach is globular and capacious, occupying much of the area of the cephalic cavity, and consisting of two distinct portions: 1, the cardiac region, surmounting the mouth and oesophagus; 2, the pyloric, placed behind the cardiac region.

Around the pylorus is situated that extraordinary apparatus of hard tubercles or sharp teeth which operate as grinding or tearing organs on the food submitted to the action of this animal mill; and though the different pieces vary considerably in different species, their greater or less development depending upon the nature of the food taken by those species, they may be traced in all the Brachyura and Macroura. In Squilla this masticatory framework is reduced to two half-horny pieces, with rounded projections; and, to make up for this deficiency, a branch of each mandible reaches down to the pyloric orifice.

From the pylorus the intestine proceeds direct to the vent, there being no convolution; but in the higher Crustaceans it is distinguishable into two portions, to which the names of duodenum and rectum have been applied, and which are sometimes, in the lobster for instance, separated by a valve, but more frequently are without defined limits. In the lower Crustaceans the intestine is cylindrical, and offers no difference throughout its whole length from the stomach to the vent, which is always situated in the last ring, and has its orifice closed by muscular fibres which perform the functions of a sphincter. The liver is largely developed in many of the Crustacea, especially in the Decapods; indeed, no one can eat a crab or a lobster without being struck with the large proportions of this viscus, which in those species is considered so delicious. In the Edriophthalmians, on the contrary, it is almost rudimentary, there being in them only three

when well developed, consists of two symmetrical portions, generally separated from each other, and composed of a collection of cæcums, which at one of their extremities discharge their secretion into excretory ducts, which being converted by their union into longer and larger vessels, pour the bile ultimately through a double channel into the pylorus. The nature of the whitish fluid secreted by the two, and, as it is said, in some cases three, elongated blind tubular wormlike organs-the first two situated on each side of the pylorus, and the third on the middle of the intestine a short way below them-is not known, nor is its use.

The two green glandular organs placed on each side of the oeso phagus are supposed to act in some degree as substitutes for salivary glands.

Much has been written on the subject of the vascular system of the Crustacea. The following are the conclusions to which Milne-Edwards and V. Audouin came, after a careful study, as well of the anatomical disposition of the circulating apparatus of the Crustacea, as of the progress of the blood through its interior:

"The circulation of the blood in these animals is accomplished in a manner very similar to what takes place in the Mollusca. The blood pushed forward by the heart, is distributed to every part of the body, from whence it is returned into large sinuses situated at no great distance from the base of the branchia; from these sinuses it is sent on to the respiratory apparatus, which it traverses, and from which it finds its way to the heart, to recommence the same circle anew. The heart is consequently aortic and single. The heart is always found in the median line of the body, and lying over the alimentary canal, near the dorsal aspect. Its form is various; in the Decapods it is nearly square, and lies in the middle and superior part of the thorax, being separated from the carapace by tegumentary membranes only, and may be seen in the space included between the two vaults of the of numerous muscular fibres, fixed by their extremities to neighbouring flanks. In structure it appears to be composed by the interlacement parts, and passing to some distance over the aggregate at either end, formed by the superposition of a number of stars the rays of which so that the whole organ brings to mind such a figure as would be do not correspond. In the other orders this general form of the heart varies considerably, from the figure of an oblong square of rather inconsiderable sure, as it occurs in the Decapoda, to that of a long cylindrical vessel extending through the whole length of the body, as it appears in the Sagoda and the Ednophthalmians. In the former of these it gives origin to six rascular trunks, three of which issue from the anterior edge, and three from the posterior surface;