288 



CLASSIFICATION OF VERTEBRATES. 



the orbit and nostril. The caecilians are tropical, occuring in 

 South America, Africa, and Ceylon, where they burrow in the 

 earth, preying upon small invertebrates. 

 The eyes, in consequence of this life, are 

 hidden under the skin. Little is known 

 of the development, except of the Cey- 

 lon ese species, IcJithyophis glutinosns, in 

 which the larva has three pairs of pectin- 

 ate external gills. In the larval TypJilo- 

 nectes the gills are saccular. Other genera 

 are Ccecilia, Rhinotrema, and HypogeopJiis. 

 No fossil species are known, but the dis- 

 tribution as well as the characters of the 

 skeleton point to a great ancestry for the 

 group. Within recent years it has been 

 supposed to be related to Amphinma, but 

 this is clearly not the case. The aisto- 

 FIG. 287. Tentacle of poda (p. 283) suggest themselves in this 



Cecilia oxyura, after connection. 

 Wiedersheim. do, duct 

 of orbital gland; dt, duct 

 of tentacular gland; e, 

 eye; m, mouth of ten- 

 tacle; ng, nasal gland; 

 og, orbital gland; r, re- 

 tractor of tentactle; tg, 

 tentacular gland. 



GRADE II. AMNIOTA (ALLAN- 

 TOIDEA). 



Vertebrates with well-developed amnion 

 and allantois ; no gills, no lateral line sys- 

 tem, and no rental portal system in the adult. 

 The amniotes derive their name from the existence during 

 foetal life of a peculiar envelope the amnion. This consists of 

 folds of the somatopleure (head, tail, and lateral folds) which 

 grow upwards on all sides of the embryo, meeting and fusing 

 above the back, so that the embryo is enclosed in a cavity 

 bounded by double walls, that nearest the embryo being the 

 amnion, the other being the chorion. The amnotic cavity is 

 filled with an amniotic fluid. Both amnion and chorion are 

 composed of ectoderm and the somatic mesothelium of the lateral 

 plates, and the space between them is an extension of the 

 coelom. With growth, the amniotic structures become connected 

 with the embryo by only a small stalk, the umbilicus, on the 



