George Albert Boulenger

“ The recent addition of a third genus of Aglossa, Hymenochirus (24) from tropical Africa, combining characters of Pipa and Xenopus, has removed every doubt as to the real affinity which connects these genera. Hymenochirus is further remarkable for the presence of only six distinct pieces in the vertebral column, which is thus the most abbreviated among all the vertebrata.
Frogs and toads occur wherever insect food is procurable, and their distribution is a world-wide one, with the exception of many islands. ”

“ The genus Arius is composed of a great number of species and has the widest distribution of all Silurids, being represented in almost all tropical countries which are drained by large rivers. Most of the species live in salt water. They possess six barbels, and their head is extensively osseous on its upper surface; their dorsal and pectoral spines are generally developed into powerful weapons. Bagarius, one of the largest Silurids of the rivers of India and Java, exceeding a length of 6 ft., differs from Arius in having eight barbels and the head covered with skin. ”

“ Other newts, and many salamanders, whether terrestrial or aquatic, pair, the male embracing the female about the fore limbs or in the pelvic region, and the males of such forms are invariably devoid of ornamental secondary sexual characters; but in spite of this amplexation the same mode of fecundation by means of a spermatophore is resorted to, although it may happen that the contents of the spermatophore are absorbed direct from the cloaca of the male. The spermatozoa thus reach the eggs in the oviducts, where they may develop entirely, some of the salamanders being viviparous. ”

“ In others, which represent the perichordal type, the greater share of the formation of the whole vertebra falls to the (paired) dorsal cartilage, but there is in addition a narrow ventral or hypochordal cartilage which fuses with the dorsal or becomes connected with it by calcified tissue; the notochord is thus completely surrounded by a thick sheath in tadpoles with imperfectly developed limbs. This mode of formation of both the arch and the greater part or whole of the so-called centrum from the same cartilage explains why there is never a neuro-central suture in these batrachians. ”

“ The teeth are not implanted in sockets, but become ankylosed with the bones that bear them, and are replaced by others developed at their bases. Teeth are present in the jaws of all known Stegocephalia and Apoda and of nearly all Caudata, Siren alone presenting plates of horn upon the gingival surfaces of the premaxillae and of the dentary elements of the mandible. But they are nearly always absent in the lower jaw of the Ecaudata (exceptions in Hemiphractus, Amphignathodon, Amphodus, Ceratobatrachus, the male of Dimorphognathus) , many of which (toads, for instance) are entirely edentulous. ”

“ In most male batrachians the testes are drained by transverse canals which open into a longitudinal duct, which also receives the canals of the kidneys, so that this common duct conveys both sperma and urine. In some of the discogloesid frogs, however, the seminal duct is quite independent of the kidney, which has its own canal, or true ureter. Many of the Ecaudata have remnants of oviducts, or Müllerian ducts, most developed in Bufo, which genus is also remarkable as possessing a problematic organ, Bidder’s organ, situated between the testis and the adipose or fat-bodies that surmount it. ”

“ It was formerly believed that the male takes charge of the eggs, and later the young, by sheltering them in the mouth and pharynx. This may still be true of some of the American species, but a long series of recent observations have shown that this most efficacious parental care devolves invariably on the female in the African and Syrian species. ”

“ Thus New Caledonia, which has a rich and quite special lizard-fauna, has no batrachians of its own, although the Australian Hyla aurea has been introduced with success. New Zealand possesses only one species (Liopelma hochstetteri) , which appears to be rare and restricted to the North Island. The forest regions of southern Asia, Africa and South America are particularly rich in species.
According to our present knowledge, the Ecaudata can be traced about as far back in time as the Caudata. ”

“ The skull, in the Apoda, is remarkably solid and compact, and it possesses a postorbital or postfrontal bone (marked 1 in the figure) which does not exist in any of the other living batrachians. The squamosal bone is large and either in contact with the frontals and parietals or separated from them by a vacuity; the orbit is sometimes roofed over by bone. The presence, in some genera, of a second row of mandibular teeth seems to indicate the former existence of a splenial element, such as exists in Siren among the Caudata and apparently in the labyrinthodonts. ”

“ The first category embraces many aquatic newts, the second nearly all the Ecaudata, the third the rest of the Caudata, and the fourth the Apoda.
In the typical newts (Molge) of Europe, the males are adorned during the breeding season with bright colours and crests or other ornamental dermal appendages, and, resorting to the water, they engage in a lengthy courtship accompanied by lively evolutions around the females, near which they deposit their spermatozoa in bundles on a gelatinous mass, the spermatophore, probably secreted by the cloacal gland. ”

“ Female salamandrids are provided with a receptaculum seminis. Copulatory organs are absent, except in the Apoda, in which a portion of the cloaca can be everted and acts as a penis. The urinary bladder is always large.
The spermatozoa have received a great share of attention, on the part not only of anatomists and physiologists, but even of systematic workers (40) . This is due to the great amount of difference in structure and size between these elements in the various genera, and also to the fact that otherwise closely allied species may differ very considerably in this respect. ”

“ Pellegrin has made the interesting observation on Tilapia galilaea that while the eggs are developing in the bucco-pharyngeal cavity the ovarian eggs are rapidly growing towards maturity, so that a fresh deposition of ova may almost immediately follow the release of the young fishes from maternal care. ”

“ The Clarias and Heterobranchus of Africa and south-eastern Asia have an elongate, more or less eel-shaped body, with long dorsal and anal fins, and are known to be able to live a long time out of water, being provided with an accessory dendritic breathing organ situated above the gills. Some species live in burrows during the dry season, crawling about at night in search of food. ”

“ In the Apoda, as in many serpentiform reptiles, one of the lungs, either the right or the left, is much less developed than the other, often very short.
Urino-genital Organs.—The genital glands, ovaries and testes, are attached to the dorsal wall of the body-cavity, in the immediate vicinity of the kidneys, with which the male glands are intimately connected. The oviducts are long, usually more or less convoluted tubes which open posteriorly into the cloaca, while their anterior aperture is situated far forward, sometimes close to the root of the lung ”

“ These journeys are occasionally of such a length that the fish have to travel all night; they are so numerous that the Indians fill many baskets of them. J. Hancock supposes that the fish carry a small supply of water with them in their gill-cavity, which they can easily retain by closing their branchial apertures. The same naturalist adds that they make regular nests, in which they cover up their eggs with care and defend them—male and female uniting in this parental duty until the eggs are hatched. ”

“ In certain of the mailed genera the secondary sexual differences may be very pronounced, and have given rise to many nominal species. The shape of the snout may differ according to the sex, and its margin may be beset with tentacles in the male, whilst it frequently happens that the head of the latter is margined with spines or bristles which are either absent or considerably shorter in the female. ”

“ In many species the sexes are dissimilar, the female being larger and less brilliantly coloured, with smaller fins; the anal fin of the male may be modified into an intromittent organ by means of which internal fertilization takes place, the ova developing in a sort of uterus. ”

“ The fourth category is represented by the Apoda or Caecilians in which, as we have stated above, the male is provided with an intromittent organ. Some of these batrachians are viviparous.
In those species in which the embrace is of long duration the limbs of the male, usually the fore limbs (pleurodele newt, Ecaudata) , rarely the hind limbs (a few American and European newts) , according to the mode of amplexation, acquire a greater development, and are often armed with temporary horny excrescences which drop off after the pairing season. ”

“ A few frogs have the skin of the back studded with stellate bony deposits (Phyllomedusa, Nototrema) , whilst two genera are remarkable for possessing a bony dorsal shield, free from the vertebrae (Ceratorphrys) or ankylosed to them (Brachycephalus) . None of the Stegocephalia appears to have been provided with claws, but some living batrachians (Onychodactylus, Xenopus, Hymenochirus) have the tips of some or all of the digits protected by a claw-like horny sheath. ”

“ Degraded, worm-like batrachians of still obscure affinities, inhabiting tropical Africa, south-eastern Asia and tropical America. Thirty-three species are known. No fossils have yet been discovered. It has been attempted of late to do away with this order altogether and to make the Caecilians merely a family of the Urodeles. This view has originated out of the very remarkable superficial resemblance between the Ichthyophis-larva and the Amphiuma. Cope (16) regarded the Apoda as the extremes of a line of degeneration from the Salamanders, with Amphiuma as one of the annectent forms. ”

“ The species which has given the name to the whole family is the “Wels” of the Germans, Silurus glanis, the largest European fresh-water fish, inhabiting the greater part of Europe from the Rhine eastwards and north of the Alps. Its head is large and broad, its mouth wide, furnished with six barbels, of which those of the upper jaw are very long. Both jaws and the palate are armed with broad bands of small closely-set teeth, which give the bones a rasp-like appearance. The eyes are exceedingly small. ”

“ The female protects them by coiling herself round the egg-mass, which the young do not leave till after the loss of the very large external gills (one on each side) ; they then lead an aquatic life, and are provided with an opening, or spiraculum, on each side of the neck. In these larvae the head is fish-like, provided with much-developed labial lobes, with the eyes much more distinct than in the perfect animal ”

“ The narrowness of their gill-openings appears to have developed in them a habit which has excited the attention of all naturalists who have visited the countries bordering upon the Atlantic rivers of tropical America, viz. the habit of travelling during seasons of drought from a piece of water about to dry up to ponds of greater capacity. ”

“ The integument of tailed and tailless batrachians is remarkable for the great abundance of follicular glands, of which there may be two kinds, each having a special secretion, which is always more or less acrid and irritating, and affords a means of defence against the attacks of many carnivorous animals. ”

“ In the majority of the Siluridae, called by A. Gunther the Proteropterae, a section extremely numerous in species, and represented throughout the tropics, the dorsal fin consists of a short-rayed and an adipose portion, the former belonging to the abdominal vertebral column; the anal is always much shorter than the tail. The gill-membranes are not confluent with the skin of the isthmus ”

“ In Paratilapia pfefferi, a fish measuring 75 mm., the eggs found in the pharynx were only about a dozen in number, and they measure 21/2 mm. in diameter. In Tilapia dardennii, which grows to a length of 240 mm., a score of eggs fills the mouth and pharynx, and each measures 5 to 6 mm. in diameter, an enormous size for so small a fish. ”

“ Of these twenty-one genera six are peculiar to tropical Africa, one to the Seychelles, four to south-eastern Asia, eight to Central and South America, one occurs in both continental Africa and the Seychelles, and one is common to Africa and South America.
These Batrachians are found in damp situations, usually in soft mud. The complete development of Ichthyophis glutinosus has been observed in Ceylon by P. and F. Sarasin. The eggs, forming a rosary-like string, are very large, and deposited in a burrow near the water. ”

“ Sundry remains from Belgium, as to the identification of which doubts are still entertained, have been regarded by M. Lohest (12) as evidence of these batrachians in the Devonian. Over 200 species are now distinguished, from the Carboniferous of Europe and North America, the Permian of Spitsbergen, Europe, North America and South Africa, and the Trias of Europe, America, South Africa, India and Australia. ”

“ Chologaster, from the lowland streams and swamps of the south Atlantic states, has the eyes well developed and the body is coloured. Amblyopsis and Typhlichthys, which are evidently derived from Chologaster, or from forms closely related to it, but living in complete darkness, have the eyes rudimentary and more or less concealed under the skin, and the body is colourless. ”