2d day of November, 1865, in latitude 25° 28′ N., longitude 41° 33′ W., making the nearest point of land 1200 miles off. They came on board in a heavy rain-squall, the clouds and ship's sails being full of them for two days, as certified to by E. G. Wiswell, master of the vessel. This species appeared in Corfu, in Spain, and even in England. The Corfu swarm, adds Mr. Scudder, was composed of the variety with yellow-colored hind-wings, and therefore came from Northern Africa, where that form is found, while the Spanish and English swarms were of the rose-colored variety, and must have originated in Senegal. "But the most interesting point of all is the fact, first pointed out by Stol, that all the other species of that group of the genus to which this species belongs are American; whence it is highly probable that A. peregrinum also is indigenous to America, from whence it has been recorded. Its occurrence in mid-ocean in such numbers is a clear indication that it originally flew from one continent to the other in sufficient numbers to establish itself in a new home."

During a late trip to the Western Territories, Professor Leidy, while watching some cliff-swallows passing in and out of their mud-built nests, was told that these nests swarmed with bed-bugs, and that people would not usually allow the birds to build in such places, because they introduced bedbugs into the houses. He collected a number of the bugs from the swallows' nests, as well as from the houses. The latter were found to be the true bed-bug; the former the Cimex hirundinis. The bugs infesting the bat and pigeon have likewise been recognized as a peculiar species, with the name of C. pipistrelli and C. columbarius. The habit of C. hirundinis was found to be similar to that of C. lectularius, the bed-bug, in the fact that the bugs during the daytime would secrete themselves in the crevices of the boards, away from the nests. After sunset he had observed the bugs leave their hiding-places, and make their way to the nests. From these observations it would appear as if the bugs peculiar to these animals (swallows and man) did not reciprocally infest their hosts.

VERTEBRATE ZOOLOGY.

By Professor THEODORE GILL,

OF WASHINGTON, D. C.

INTRODUCTORY.

The usual activity has been manifested during the past year by laborers in the different fields of Vertebrate Zoology. Memoirs have been published on the Morphology and Comparative Anatomy of different systems and parts, many articles have been devoted to Faunal Zoology, and numerous new species have been described, although of the latter fewer, perhaps, have been made known than on the average have been introduced during past years. The tendency to admit a wider range of variation, and to refuse specific rank to slight differences is becoming general, and this will operate in future to diminish the number of new species as well as to degrade many old ones. A notable example of the difference now-from the past-in the mode of treatment of variations has been recently furnished by memoirs of Messrs. J. A. Allen and E. R. Alston on the Squirrels of the Tropical Regions of America. According to Mr. Alston, no fewer than fifty-nine (59) specific names have been at one time or another proposed for forms occurring in the region in question; but these have now been reduced by Messrs. Alston and Allen, after independent examination of very rich material and of almost all the previously described types, to twelve species.

In the richness of the material at hand, it has not been easy to select that which might be regarded as of greatest value or interest from the mass of contributions to Vertebrate Zoology during the year. Abstracts have been chiefly made of those memoirs which are of special interest on account of the relations of the facts which they exhibit to problems of morphology, or from the light they throw on homologics; of those whose interest is inherent by reason of the popularity or well-known character of the animals in

question; and of those which relate especially to the American fauna, and thus concern every native naturalist.

Origin of Vertebrate Limbs.

Various views have been entertained respecting the genesis and development of the limbs of Vertebrates. That most prevalent twenty years ago, or more, was one especially maintained by Professor Owen, namely, that they were diverging appendages of special arches, the anterior or pectoral being the "ribs " or " pleurapophyses" of the occipital arch, and the posterior having corresponding relations with the pelvic arch. This, however, was long ago shown to be untenable. Recently several naturalists (e. g., F. Balfour, J. K. Thacher, and St. George Mivart) have become satisfied that the limbs were originally developed from lateral fins of the same nature and parallel with the dorsal and anal, and that, in the words of Balfour, they are 66 remnants of continuous lateral fins." Balfour was led to this conclusion by the study of the embryonic development of Selachians, while Thacher and Mivart have reached the same result chiefly from the investigation of the grown forms of the same class, and the likeness and essential similarity of structure of the lateral and median fins. There can be, in fact, very little doubt that the view of these naturalists named is the correct one, and, this being adopted, all the facts of development and modifications of the limbs harmonize. In the lowest of the Vertebrates-the Leptocardians, i. e., Amphioxus and Epigonichthys-there are lateral folds, one on each side, of the same character as the dorsal and anal folds, designated as fins; and doubtless the nature of the limbed fins would have been recognized before had not the Marsipobranchiates intervened between the Leptocardians and the Selachians. All living Marsipobranchiates have eel-like forms and are destitute of lateral fins; and this negative character, which is probably simply the result of the elongated form and an atrophy or loss, has been insensibly taken as a principal feature of the class. In truth, however, the form is no more to be considered as a necessary element of the Marsipobranchiate type than is the eel-like form of the Teleost, and we must recognize in the living Marsipobranchiates simply modified and divergent derivatives of a type which doubt

less was originally characterized by the development of lateral fins. The higher forms of Vertebrates manifest successive deviations from this primitive type.

In the Selachians, the lateral fins are low down on the sides or inferior, and the plane of their surfaces is nearly horizontal.

In the Ganoids, they evince more or less of a tendency to change the plane from horizontal to oblique-less in the Chondroganoids; most in the Amiids.

In the Teleosts, pectoral fins are advanced still higher up on the sides, becoming, on the whole, more and more elevated as the forms diverge from the Ganoids, and become specialized as thoracic and jugular Teleocephali.

The endoskeletal bases of the limbs are supposed to have originated from ingrowth of the pair-finned skeleton at definite areas, and the composite structures evidenced in the pectoral, and probably pelvic girdles, have apparently resulted from ingrowths at different stages. If, for example, we compare the shoulder girdle of the Selachians with that of the Ganoids and the Teleosts, we find that the first is quite simple, and it evidently represents only the inner elements of the girdle of the last two types. If the sturgeons are considered, it becomes plain that exostosis, or development of bone externally, has first supervened, and that this has subsequently penetrated inwards, and become closely identified with the inner or coracoid elements. (See Gill, "Arrangement of Families of Fishes," p. 9, 1872).

The process of differentiation between fins and the limbs of Terrestrial Vertebrates is best explicable by reference to the Polypterids. In those fishes, the pectoral fin is supported by two elongated bones connected with a basal cartilage. This basal cartilage apparently represents the humerus, and the succeeding bones the radius and ulna of the land Vertebrates; while in the specialized fishes, first the humeral rudiment disappears, and then the radial and ulnar, leaving, in most of the Teleosts, only the several parallel bones at the base of the fin, which are, apparently, homologous with the metacarpal, the carpal probably having been developed in the undifferentiated cartilage intervening in the Polypterids between the radial and ulnar elements.

U

Fishes, etc.

A goodly number of contributions have been made to the literature of Ichthyology in most of its branches. The Selachians have received special attention, and members of the class have been examined as to skeletal characters, by C. Hasse, A. Goette, W. K. Parker, and St. George Mivart; as to the nervous system, by E. Ehlers and J. V. Rohon; and for the embryology, by J. M. Balfour; while certain species. have been elucidated by Garman, of Cambridge, Mass. The true fishes have also received a due share of attention from anatomists (although less proportionately than the Selachians), and the faunas of several regions have been especially studied, such as the fresh-water fishes of North America, by E. D. Cope and D. S. Jordan; the marine species, by G. B. Goode, T. Bean, and H. C. Yarrow; those of the Arctic regions, by C. Lütken; deep-sea forms, by A. Günther; Japanese types, by A. Günther and F. Hilgendorf; South American fresh-water forms, by F. Steindachner and C. Lütken; African fresh-water species, by C. Dombeck; Indo-Moluccan species, by P. von Bleeker; and Australian types, by T. Castelnau, Hector, and W. Macleay. Quite a large number of new genera" have been proposed, but several of them are unquestionably the result of imperfect knowledge or erroneous ideas, and among such may be mentioned those named by Count Castelnau (1) Brisbania and (2) Baridia or Beridia. The former was proposed for a fish occurring in the Brisbane River (New South Wales), and is undoubtedly identical with Megalops, while the latter is the same as Gnathanacanthus, long before described by Bleeker. The embryology of different species has been investigated by A. Agassiz, Carlo Emery, C. Kupffer, and E. Van Beneden. Death has deprived ichthyology of the most active and one of the most useful laborers of the century, in the person of Dr. P. von Bleeker.

66

North American Fresh-water Fishes.

Professor Jordan during the past year continued his investigation of the fresh-water fishes of North America, and has given his latest views in a catalogue of all the recognizable forms. Six hundred and sixty-five species are admitted-many, however, with doubt; and these represent, ac