588 CHORD AT A. 



lata are viviparous, the former undergoing its metamorphosis inside tlie 

 mother. 



Order IV. Anura. 



The anura have the compact bodies famiHar in frogs and toads, 

 with a small number (7-'.)) of trunk vertebras and complete absence 

 of tail; the caudal vertebras being represented by a long bone, the 

 urostyle. Eibs are sometimes distinct, sometimes fused to the 

 transverse jn'ocesses ; the limbs are larger than in other Amphibia, 

 and are frequently used for leaping and climbing. Ear drum and 

 tymjianic membrane are lacking only in the Pelobatidas; their 

 presence is correlated with the existence of vocal cords and the pro- 

 duction of sound. The metamori^hosis includes a tadpole stage. 



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

 unpaired opening of the Eustachian tube. Pijja (p. 585), South America ; 

 Dactijlethra, Africa. 



Sub Order II. ARCIFEEA. Tongue present, Eustachian tubes widely 

 separate, coracoids of the two sides overlapping. BuroxiDiE, toads, tooth- 

 less ; Buffi* the dermal glands poisonous. PELOBATro.E, with teeth, 

 usually no tympanum. HcaTpMopus* burrowing toad, with tympanum. 

 Hylid^, tree toads, toothed ; tips of toes with sucking discs ; Hyla*Acris.* 



Sub Order III. FIRMISTERNIA. Tongue present, Eustachian tubes 

 distinct, coracoids firmly united in the middle line. Eanid.e, frogs. 

 Rana r.atesbiana* bull frog, the largest frog known ; numerous other 

 American species. 



Series II. Aiiniota. 

 Vertebrates with amnion and allantois (p. .554:) in embryonic 

 life; with the pro- and mesonephros functional only in the em- 

 bryos, and rei^laced in the later stages by the true kidney (meta- 

 nephros) ; ducts of the embryonic excretory system retained only 

 so far as they have genital functions ; gill slits appearing as trans- 

 itory structures, but without gills and never functional. There 

 are two great divisions of the Amniotes, the Sauropsida and the 

 Mammalia. The Sauropsida include the IJejitilia 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 jaM's ; ankle joint between the first and second rows of 

 tarsals; the presence of epidermal scales, nucleated red blood 

 corpuscles, and a cloaca. 



Class I. Reptilia. 



On account of similarity of form, the reptiles and Amphibia 

 were long united. They form parallel groups: urodeles and liz- 

 ards, frogs and turtles, c;ecilians and snakes. Hence the points 



