ir,8 



Comparative Morphology of Chordates 



anurans, the "Goliath frog," the total length of head and trunk is 

 about 12 inches. 



The Anura are divided into several (Noble makes 11) families 

 whose many species make up the great majority, perhaps nine tenths, 

 of the species of amphibians. The common toad, Bufo americanus, 

 is of the Family Bufonidae. The Family Banidae includes many of 

 the more common frogs of the northern hemisphere — Rana clami- 

 tans, the green frog; B. pipiens, the leopard frog; B. catesbiana, 

 the aquatic bullfrog. The Family Hylidae includes tree frogs (or tree 

 toads), noted for their ability to change color — e.g., Hyla versicolor. 



Order Apoda (Gymnophiona) 



This smallest of amphibian orders includes animals which might 

 easily, at first glance, be mistaken for small snakes or for earthworms 



: mm^ 



Fig. 355. Siphonops, one of the Apoda. 

 (Courtesy, Brehm: "Tierleben," Leipzig, 

 Bibliographisches Institut.) 



10 or 12 inches long (Fig. 355). Their amphibian nature is revealed by 

 the fact that most of them pass through the typical larval stage of 

 amphibians. A metamorphosis takes place, during which the three 

 pairs of external gills are absorbed, the clefts are closed, and the tail 

 is nearly or quite absorbed so that the cloacal aperture of the adult is 

 at or very near the hind end of the long cylindric body. No trace of 

 legs appears in either adult or larva. In some members of the Order 

 the larval stage is omitted. It is a noteworthy fact that the embryonic 

 pharyngeal pouches of the most anterior pair, corresponding to those 

 which become the spiracles of sharks, are temporarily open to the 

 exterior in the larva. So far as known, this does not occur in other 



