« EelmineJätka »
the basal joint of each. These areas constituted respectively the scraper and the rasp: the former was tolerably thickly but regularly beset with stout, conical sharp spinules curved like a tiger's canine, only more towards the points, some of which terminate in a long limp hair; the latter thickly studded with minute tubercles shaped like tops of mushrooms.
It now remains for Mr. Wood or some one else to discover the ears of the scorpion; for if they can produce a sound, they must have ears to hear it, and none are as yet known to exist in the Arachnida.
In insect anatomy, an elaborate memoir on the so-called ventral vessel of the Lepidoptera, with observations on the sympathetic nerve, has been published in Hofmann's Niederländisches Archiv für Zoologie (Bd. iii., Heft 2, 1876). The examination of these organs was made in examples of all the families from the Papilionido to the Pterophoridæ.
A memoir on the internal spinning apparatus of Lepidopterous insects, by Helm, appears in Siebold and Kölliker's Zeitschrift (vol. xxvi.).
Dr. O. J. B. Wolff has published in the “Nova Acta Acad. Natur. Curios.," vol. xxxviii., Dresden, 1876, a memoir (illustrated with eight plates) on the minute anatomy of bees, with reference especially to the mechanism of the mouthorgans and respiratory organs of the thorax and abdomen.
An elaborate and richly illustrated memoir on the sense-apparatus of the Orthoptera, by Dr. V. Graber, appears in the Transactions of the Imperial Academy of Science of Vienna.
Dr. C. Chun has studied the structure, development, and physiology of the rectal glands of insects. His memoir, with three plates, is in the Transactions of the Frankfort Scientific Society.
Evolution. Among communications of theoretical interest are articles by Mr. W. H. Dall, “On a Provisional Hypothesis of Saltatory Evolution,” and by Dr. W. K. Brooks, entitled “A Provisional Hypothesis of Pangenesis,” both published in the American Naturalist.
• Parthenogenesis. That fishes and other vertebrates have in two or three observed cases been partially developed without fecundation
is on record. Dr. E. L. Sturtevant, on removing (March 15) some eggs from a pickerel, found that some of the egg “had evidently developed in the line of the fecundated egg, as the cells were arranged in the form of a curled fish, thè line of the back being well defined, the line of the belly and sac poorly or not at all defined, while there was a concentration of cells about the locality of the eye. I cannot say that I saw a young fish, for I did not, but I saw what I considered sufficient to interpret as development to a certain degree without fecundation.” The account in full appears in the American Naturalist for August; and in a succeeding number Professor W. K. Brooks gives a history of what is known on this subject.
VERTEBRATES.* Progress in Vertebrate Zoology has been essentially similar to that in past ordinary years. No discovery of a startling character has been made, but the usual activity has been manifested in the search for and description of new species, in the more or less careful elaboration of small groups and faunas, and in anatomical studies of special forms. We here confine ourselves to notices of a few contributions which have a general interest, or relate to the North American fauna.
The Limits of the Branch of Vertebrates and its Classes. Until quite recently, and since Cuvier first established the “embranchement” of Vertebrates, the group so designated was accepted without hesitation with the limits originally given to it. Charles Bonaparte, the Prince of Canino, had, indeed, in 1856, proposed to relegate to the branch the vermiform Sagitta as the representative of a peculiar class exhibiting a retrograde metamorphosis; but the suggestion fell still-born, and no further attention has been paid to it. Lately, however, there has been a disposition to modify the limits of the branch in opposite directions. Semper, for example, wished to eliminate Branchiostoma (Amphioxus), or the class of Leptocardians, from the group, while others have been disposed to approximate to it the Trinicates, which for
By Professor Theodore Gill, of Washington, D. C.
a long period were regarded as Mollusks. These diverse tendencies have been both exemplified during the past year.
On the one hand, like Semper, Mr. Hoppe-Seyler urges the separation of Branchiostoma from the Vertebrates, and expresses surprise that systematic zoologists should have so readily associated the type with the members of that branch; he contends that the Cephalopods are even nearer the Vertebrates than is Branchiostoma, and affirms that the form in question has nothing in common with the Vertebrates but the chorda dorsalis and the development of the venous system above it and the alimentary canal below: “It differs," he says, “from the Vertebrates in having no brain, no closed vascular system with red blood-corpuscles, no bile-secreting liver, and no gelatin-yielding tissue.” In consideration of these deviations and the facts in the development and composition of the tissues of animals generally, he arrives at the conclusions noted adverse to the association of Branchiostoma with the Vertebrates. On the other hand, Professor E. Ray Lankester, of Oxford, in “Notes on the Embryology and Classification of the Animal Kingdom," published in the Quarterly Journal of Microscopical Science for October, 1877 (vol. xvii., p. 399–454), has claimed not only Branchiostoma, but also the Tunicates, to be representatives of the Vertebrate branch-or “phylum,” as he prefers to call it; and forms for the Tunicates, under this phylum, a “branch " named Urochorda, co-ordinate with two other branchesCephalochorda, represented by Amphioxus, and Craniata, constituted by all the remaining Vertebrates. He thinks, like Dr. Anton Dohrn, that evolution may tend in different directions, and that, although on the whole it is in the direction of progression from the low to the high, it may be, and in a number of cases he believes actually has been, towards degradation. “So strong," says he,“ is the case in favor of degeneration, that at present all that can be said against it and in favor of progression, with regard to any particular case, is this—that the general doctrine of evolution justifies us in assuming, at some period or other, a progression from the simplest to the most complicated grades of structure; that we are warranted in assuming at least one progressive series leading from the monoplast to man; and that until we have special reason to take a different view of any particular
case, we are bound to make the smallest amount of assumption by assigning to the various groups of organisms the places which they will fit into, on the supposition that they do represent in reality the original progressive series. ... When, therefore, the hypothesis of degeneration presents itself as a solution of any special morphological difficulty, we need have no scruples or prejudices in favor of the doctrine of universal progression which should prevent us from accepting it.” Thus reasoning, he urges that the Tunicates are degraded Vertebrates; that their systematic relations with the members of that group are evidenced by the chorda of the larval stage; and that there has been quite a general tendency towards degeneration in these animals.
Professor Lankester has further expressed his views of the classification of the Vertebrates, as well as other types of the animal kingdom, in the following condensed arrangement:
BRANCH A.—UROCHORDA. (1.) I. Larvalia (“Tunicates” of genera Appendicularia
and Kowalewskyia). (2.) II. Saccata (“Tunicates” of typical form).
Branch B.-CEPHALOCHORDA [=Leptocardia, Haeckel]. (3.) I. Leptocardia (=Acrania, Haeckel]. BRANCH C.-CRANIATA [=Pachycardia, Haeckel].
Grade A.-Cyclostoma (Monorrhina [Haeckel]). (4.) I. Hyperotreta. (5.) II. Hyperoartia.
Grade B.—Gnathostoma (Amphirrhina [Haeckel]). Sub-grade A.—Heterodactyla branchiata [ = Lyrifera, Gill]. (6.) I. Pisces (with sub-classes Selachii, Holocephali, Ga
noidæ, Teleostei). (7.) II. Dipnoi. Sub-grade B.-Pentadactyla branchiata [ = Batrachopsida,
(8.) I. Amphibia (with sub-classes Lissamphibia [=Urodela and Anura) and Phractamphibia [=Laby
Branch A.-MONOCONDYLÆA [=Sauropsida, Gill].
ria, Pterosauria, Dicynodonta, Ornithoscelida,
and Crocodilia. (10.) II. Aves.
Branch B.-AMPHICONDYLA [=Malleifera, Gill]. (11.) I. Mammalia ( with three grades, viz., Cloacalia
[=Monotremata), Marsupialia, and Placentalia, and with six sub-classes under Placentaliaviz., Edentata, Ungulata, Proboscidea, Chelophora [=Hyracoidea), Carnaria [=Carnivora +Pinnipedia+Cetacea] and Discoplacentalia).
A few remarks as to the issues involved may be in place here.
It is safe now to affirm very positively that Branchiostoma has been generally, until lately at least, associated altogether too closely with the craniate Vertebrates, and that there can be no doubt but what the hiatus between it and the typical Vertebrates is greater than is that between any other classes of the branch. The facts remain, however, that morphologically Branchiostoma is by far more readily comparable with the Marsipobranchiate Vertebrates than with any other type, and that as to most of its peculiarities of organization, it is not now difficult to appreciate the homologies with the several systems in the latter: the denial of the title of Branchiostoma to rank among the Vertebrates because certain physiological functions are not carried on as in the higher Vertebrates is a denial of the now generally recognized dogma that physiology must not be allowed to interfere with morphology in our appreciation of the relations of living beings. We must admit that Branchiostoma is not only not a fish, but quite remote from the true fishes; but it certainly seems to be more nearly related to the Vertebrates than other animals, and, in fact, to be a