THE PRIMEVAL SALAMANDERS 



2681 



and the accompanying figure; these canals also occurring in certain fishes. So 

 far as can be ascertained, both external and internal gills generally disappeared 

 in the adult. Varying from the size of a small newt to that of a crocodile, 

 the primeval salamanders are of especial interest to the evolutionist, as it is 

 pretty certain that not only are they the descendants of primeval fishes, but that 

 they are the ancestors both of the modern Amphibians and the extinct Anomodont 

 Reptiles. And it is probable that Mammals have originated, either directly from 

 them or from a lost group intermediate between them and the Anomodont Reptiles. 

 They appear to have been spread over the whole globe, and they have been divided 

 into several subordinal groups. Among these the 

 highest are the true L,abyrinthodonts, typically 

 represented by the gigantic Mastodonsaurus and the 

 somewhat smaller Metoposaurus of the Trias. These 

 were crocodile-like animals, generally with disc-like 

 vertebrae in the adult, the teeth more or less plicated, 

 and the surface of the skull marked with sculpture 

 and mucous canals. In the Permian Archegosaurus, 

 the vertebrae were, however, of the complex primitive 

 type. The Gilled L,abyrinthodonts, as represented 

 .by Protriton and Pelosaurus, are a group of much 

 smaller forms, characterized by their barrel-shaped 

 vertebrae, pierced by a remnant of the canal of the 

 primitive notochord; short and straight ribs, artic- 

 ulating by a single head; simple teeth, and the 

 absence of ossification in the occipital region of the 

 skull, as well as in the wrist and ankle joints; a fur- 

 ther point of distinction being the development of internal gills in the young. The 

 Permian and Carboniferous Snake-like Labyrinthodonts are characterized by the 

 snake-like form of the body, and the apparent absence of limbs. The vertebrae were 

 elongated and without spines, while the ribs were slender and barbed like those of 

 fishes, and the teeth smooth and simple. Probably the external gills persisted 

 throughout life. In Britain the group is represented by the small Dolichosoma; but 

 Pal&osiren of Bohemia is estimated to have been over forty feet long. If these crea- 

 tures prove to be the ancestors of the worm-like Amphibians, it would show that 

 the latter are distinct from the newts and salamanders. The Microsauria include 

 small lizard-like forms, such as Ceratoerpetum and Hylonomus from the Carbonifer- 

 ous of Europe and Nova Scotia, which appear more highly organized than the pre- 

 ceding, and thus connect the Amphibians with the Beaked Reptiles. Their 

 vertebrae are long and constricted, with traces of the notochord; the ribs are gener- 

 ally long, curved, and two headed; the teeth have large central pulp cavities, but no 

 plications; the occiput is ossified, but the wrist and ankle are either ossified or car- 

 tilaginous, and in some cases the back is covered with bony scales. In several forms 

 the bony scales on the under surface are so slender as to assume the appearance of 

 abdominal ribs like those of the Beaked Reptiles. 



SKUI.I, OF THE METOPOSAUR. 

 (One-third natural size.) 



