favourite object of attachment to all this group; here grow, but not too closely together, several aquatic plants,- water crowfoot, amphibious Persicaria, the copper-coloured Potamogeton (P. perfoliatus) with transparent leaves like goldbeater's skin, and other plants of the water.

Now let us go to some sheltered spot or corner of this great pool, to which the wind has blown all the floating rubbish, tangled masses of Confervæ, decayed roots of grasses, feathers of birds, etc., and dip our bottles into this heterogeneous mass. Never mind the ironical smile of yonder angler, who, proud of the pike of twelve pounds weight which he has just succeeded in landing about twenty yards from us, accosts himself in rather a loud tone with "What, in the name of fortune, can that fellow be grubbing after?" No doubt you represent in his mind that very eccentric old fellow who, as sung by the author of the "Ingoldsby Legends,"

"Would pore by the hour

O'er a weed or a flower,

Or the slugs that come crawling out after a shower.

With nasty long tails arm'd with nasty long stings."

You are used to this sort of thing, and continue your dabbling in spite of it all. Now look into your bottle, and you will see several small, dark, round bodies, about the size of a pin's head perhaps; take three or four out, and examine them singly on your hand with your lens. They are slightly convex on one side, and concave on the other." "Then they are of no use except as indicators; they are merely the separated discs or faces of old specimens; try again." "Now what have you?" "Why, a mass an inch long, and of an oval shape." "These agglomerated masses are to be depended on, so we will take them home, and in due time you will see them germinate." These little bodies are the product of the most beautiful of all the Fresh-water Polyzoa, and of one which is generally considered to be somewhat rare, viz., Cristatella Mucedo, the only locomotive species; for, unlike the rest of the family, Cristatella is unattached, and being possessed of a muscular base, strongly resembling the foot of a gasteropodous mollusc, the colony is enabled to move about, slowly, it is true, upon the surface of submerged weeds, stones, etc. But it is extremely difficult to detect the presence of adult forms of Cristatella, on account of their transparency, and the fact that they live for the most part upon weeds which

are generally covered with scum, and the faded filaments of Algae of the same colour as the animals. Therefore, if you are desirous to learn whether any mill-pool or lake contains Cristatella, the better plan is to search for these round black bodies (which Professor Allman has designated Statoblasts) late in the autumn, or in winter, or in early spring, rather than for the mature animals. The same advice, too, will be found good in the case of other Polyzoa. These statoblasts are always to be found, and generally in very great abundance, floating in the water, so that all that is necessary is, to dip your collecting bottle in, or to skim the surface; the statoblasts are so characteristic of the different species to which they belong, that you can never doubt what kinds your pond supplies.

If, however, the fully-developed colony is the object of your search-I am speaking of Cristatella,- then in the months of June, July, and August you should visit the pond. And here let me give a bit of advice: lie flat down (the Cristatellæ are almost always within a few feet of the bank, covered by water varying from an inch in depth to about two feet), and with your eyes close to the surface of the water, and with as little disturbance of it as possible, gently clear away the floating weeds, and examine the submerged stems of the plants in situ, just as they grow in the water; it is of little use to pull the weeds out of the water, and then examine them, because it is almost impossible amid the converfoid growth which covers the plants to detect the collapsed form of your much prized Cristatella, so you must "stoop to conquer." Probably for a minute or two you will see nothing like the object of your search; but be patient, continue to gaze, and you will most likely be rewarded by observing, amid the scum and confervæ, an oblong-shaped feathery object, about one inch or more in length perhaps, of a pale yellow colour, bearing some resemblance to the well-known gelatinous egg nidamentum of Limneus stagnalis. This is Cristatella Mucedo, the queen of Polyzoa; and if you are not gratified at the sight of her extreme beauty, as you gently place her with the weed to which she is attached in your collecting bottle, and if you have not an intellectual treat over your microscope when you get home, it is clear you are no judge of beauty.

The attached forms of the Fresh-water Polyzoa are not nearly so difficult to find; at least, I speak of those species with which I am familiar-such as Alcyonella fungosa, very readily found and common everywhere, three or four kinds of Plumatella, and Fredericella Sultana. This last-named species appears to be a singular exception, in one respect, to the rest; for while they seem to be strictly annual in their duration of existence, Fredericella is perennial. At any rate, I have discovered it in mid-winter,

and at all other periods of the year; and that this species is perennial is rendered probable by the fact that the statoblasts are very sparingly produced when compared with the immense profusion yielded by other kinds. The attached forms of the Fresh-water Polyzoa are readily found, if the collector will patiently examine submerged branches of trees, or the under-side of leaves and stones; for the large sponge-like masses of Alcyonella, the branching tubes of Plumatella, and the tangled interlacements of Fredericella are apparent to the eye without an effort-though at the same time, perhaps, if he had never seen a single specimen, he would either not notice them or would fail to discern in them objects of much interest.

The Polyzoa afford a most instructive example of the necessity to pay particular attention to the internal structure and anatomy of any animal, if we would desire to ascertain its place in the animal kingdom. In external form the members of this group bear a very close resemblance to phytoid Zoophytes with which indeed they were long confounded. Now these latter animals belong to the low-organized class known by the name of Hydrozoa, of which the common Hydra or Fresh-water Polype, may be taken as the type. But the Polyzoa, notwithstanding their resemblance to, are widely separated from this group, and represent in their structure analogies with that section of the molluscan sub-kingdom happily designated by Milne Edwards Molluscoida. "You go down," says Mr. Kingsley, "to any shore after a gale of wind, and pick up a few delicate sea-ferns. You have two in your hand (Sertularia operculata and Gemellaria loriculata), which probably look to you, under a good pocket magnifier, identical, or nearly so. But you are told, to your surprise, that however like the dead horny polypidoms which you hold may be, the two species of animals which have formed them are at least as far apart in the scale of creation as a quadruped is from a fish."* The Polyzoa have now been admitted to their proper place in the animal kingdom, and have been advanced from the sub-kingdom Radiata (now Calenterata) to that of the Mollusca. "Thus," as Dr. Carpenter instructively remarks, "whilst microscopic research has degraded the Foraminifera from their supposed rank with the nautilus and cuttle-fish to the level of the sponge, it has raised the wheel-animalcules into proximity with aquatic worms and the humble sea-mat' (flustra), formerly supposed to be a plant, to a position not much below that of the oyster and mussel."+

The Polyzoa having an organization homologous with the

*Glaucus, p. 33.

"The Microscope and its Revelations," p. 18, 2nd ed.

Ascidiæ, or tunicated Molluscs, are now accordingly included with this latter group, and form together the section Molluscoida, (the other section being the Mollusca properly so called). A glance at the illustrations will show the general resemblance which exists between a Polyzoon and an Ascidian, but for the determination of the precise homologous organs the reader must refer to Professor Allman's valuable monograph.*

In the Ascidian the respiration takes place by means of internal branchia; in the Polyzoon, by means of external branchiæ forming around the mouth a corona of tentacles ciliated and protractile. They have both a distinct digestive tube, which turns on itself and is open at both extremities; the nervous ganglion, though it does not occupy the same position in both animals, is of similar form and of a very rudimentary nature, and is regarded by Allman as a further instance of homology. The most marked point of difference between the organization of a Polyzoon and a tunicated Mollusc consists in the latter animal being possessed of a heart and a vascular system, while in the Polyzoon no trace of anything of the kind

exists.

It will be well now to obtain some general conception of a Polyzoon, which we shall be readily able to do with the figures before us (Plate XIII., figs. 1 and 2), and from the following clear explanation of them by Professor Allman :—

"Let us imagine an alimentary canal, consisting of oesophagus, stomach, and intestine, to be furnished at its origin with long ciliated tentacula, and to have a single nervous ganglion situated on one side of the oesophagus. Let us now suppose this canal to be bent back upon itself towards the side of the ganglion, so as to approximate the termination to the origin. Further, let us imagine the digestive tube thus constituted to be suspended in a fluid contained in a membranous sac, with two openings- one for the mouth and the other for the vent-the tentacula alone being external to the sac. Let us still further suppose the alimentary tube, by means of a system of muscles, to admit of being retracted or protruded according to the will of the animal, the retraction being accompanied by an invagination of the sac, so as partially or entirely to include the oral tentacula within it; and if to these characters we add the presence of two sexual organs in the form of ovary, and testis, occupying some portion of the interior of the sac, and the negative character of the absence of all vestige of a heart, we shall have, perhaps, as correct an idea-apart from all theoretical considerations of homology or derivation from an archetype-as can be conveyed of the essential structure of a Polyzoon in its simplest and most generalized condition.

"To give, however, more actuality to our ideal Polyzoon, we may bear in

"On the Fresh-water Polyzoa.". Ray Society, 1856. tie., Correspondence of parts,

mind that the immediately investing sac has the power, in almost every case, of secreting from its external surface a secondary investment of very various constitution in the different groups; and we may, moreover, conceive of the entire animal with its digestive tube, tentacula, ganglion, muscles, generative organs, circumambient fluid, and investing sacs, repeating itself by gemmation, and thus producing one or more precisely similar systems, holding a different position relatively to one another, while all continue organically united, and we shall then have the actual condition presented of the Polyzoa in their fully developed state."

*

Now of these two investing tunics, the outer one is called the ectocyst, the inner the endocyst. This latter tunic lines the interior of each chamber, and terminates in the tentacular crown (lophophore‡); it is transparent, and is readily seen in all the Fresh-water Polyzoa, both when the animal is protruded, and when it is retracted within its cell; for a portion of the endocyst always remains" in a permanently invaginated state." The ectocyst, in most of the genera, consists of a tough leathery substance, imbedded in which are silicious and other earthy particles. In Fredericella I have noticed that the silicious "frustules," or component cells of Diatomacea, especially those of Diatoma vulgare, enter largely into the composition of the ectocyst; Cristatella alone appears to be destitute of an ectocyst. The inhabitant of each cell is called a Polypide,§ a term wisely proposed by Allman instead of Polype, which should now be confined to the animals belonging to the Radiata; the whole dermal system of a colony is known by the name of cœnæcium.|| The very curious valve-like organ, like a tongue, which arches over the mouth, and which all the fresh-water species, except Paludicella, possess, has received the name of epistome. The presence or absence of this organ, whose function, by the way, it is difficult to determine, gives the name of the order to which the numerous species respectively belong. Those Polyzoa which are furnished with a bilateral tentacular disc, and whose mouth is provided with the tongue-like organ described above, are placed in the order Phylactolaemata,** to which are referred all the fresh-water species, except Paludicella, and none of the marine except Pedicellina; while the species destitute of an epistome, and which have a circular tentacular crown, belong

* i.e., Budding.

+ Ectocyst, from the Greek ectos, "outside," and cystis, a “bladder,” or "bag." Endocyst, from endos, " inside," and cystis.

From lophos, "a crest," and phoreo, “I bear."

§ From polypous, "a polype," and eidos, "resemblance." From coinos, "common," and oicion, "a house."

¶ From epi, "upon," and stoma, 66 a mouth." ** From phylasso, "I guard," and laima, "the throat."