520 CHORDATA 



tail Ribs are present, but so short that they do not reach the sternum, which 

 is weakly developed or is entirely absent. Tympanum and Eustachian tube 

 are entirely lacking, as are the vocal cords and the production of sound. 



Sub Order I. PERENNIBRANCfflATA. Two or three gill slits, three 

 bushy gills, and a swimming tail persist throughout life. Necturus* mud 

 puppy, with legs and two gill slits. Siren,* three gill slits, hind legs lacking ; 

 Typhlomolge* Typhlotriton* both blind, from caves and underground waters of 

 V . S. Sub Order II. DEROTREMA. External gills lost, but an opening in 

 the neck leading to the gill slits. Menopoma* (Cryptobranchus) , hellbender, 

 legs strong; A mphiuma* legs rudimentary. Sub Order III. SALAMANDRINA. _ 

 A'Fter the loss of gills the gill slits close. Amblystoma* (fig. 5), A. tigrinum 

 and the Mexican axolotl breed in the larval stage. This and other facts leads 

 to the view that possibly the Perennibranchs are all neotenic (p. 150). Pletho- 

 tl.ni* Spelerpes* Salamandra. 



Order IV. Anura. 



The anura have the compact bodies familiar in frogs and toads, with a 

 small number (7-9) of trunk vertebras and complete absence of tail, the caudal 

 vertebra being represented by a long bone, the urostyle. Ribs are sometimes 

 distinct, sometimes fused to the transverse processes; the limbs are larger than 

 in other Amphibia, and are frequently used for leaping and climbing. Ear 

 drum and tympanic membrane are lacking only in the Pelobatidae; their presence 

 is correlated with the existence of vocal cords and the production of sound. 

 The metamorphosis includes a tadpole stage. 



Sub Order I. AGLOSSA. Toad-like anura with degenerate tongue and 

 unpaired opening of the Eustachian tube. Pipa (p. 518), South America; 

 Dactylethra, Africa. Sub Order II. ARCIFERA. Tongue present, Eustachian 

 tubes widely separate, coracoids of the tw T o sides overlapping. BUFONITXE, 

 toads, toothless; Bufo,* the dermal glands poisonous. PELOBATID^E, with teeth. 

 Scaphiopus,* burrowing toad, with tympanum. HYLID.E, tree toads, toothed; 

 tips of toes with sucking discs; Hyla* Acris* Sub Order III. FIRMISTER- 

 XIA. Tongue present, Eustachian tubes distinct, coracoids firmly united in 

 the middle line. RAXUXE, frogs. Rana* 



SERIES II. AMNIOTA. 



Vertebrates with amnion and allantois (p. 490) in embryonic life; 

 with the pro- and mesonephros functional only in the embryos, and re- 

 placed in the later stages by the true kidney (metanephros) ; ducts of the 

 embryonic excretory system retained only so far as they have genital func- 

 tions; gill slits appearing as transitory structures, but without gills and 

 never functional. There are two great divisions of the Amniotes, the 

 Sauropsida and the Mammalia. The Sauropsida include the 

 Reptilia and the Aves, which agree with each other and differ from the 

 mammals in having a single occipital condyle, the quadrate acting as 

 suspensor of the jaws; ankle joint between the first and second rows of 

 tarsals; the presence of epidermal scales, nucleated red blood corpuscles, 

 and a cloaca. 



