GYMNOPHIONA. 187 



Fossil remains of this group first appear in the Tertiary period, 

 with the exception of the extinct family of the Lalii/rinthodonta 

 (Mastodonsaurus) which belongs to the Trias. 



Order 1. APODA* (GYMKOPHIONA). 



Vermiform Amphibia covered with small scales, without limbs, 

 with biconcave vertebrce. 



The external skin of the Gfymnophiona, which were for a long 

 time classed with the Snakes, contains small scales which are arranged 

 in transverse rings (tig. 628). The internal organisation and the 

 transitory branchial respiration, however, places them amongst the 

 Amphibia, of which group they are in many respects, the most lowly 

 organised. This is especially the case with the skeleton, which is 



IG. 628. Siphonojm mexicana (regne animal). 



distinguished by the biconcave form of the vertebrae and the per- 

 sistent notochord. The bony skull, which has two condyles, is firmly 

 united to the facial bones, of which the maxillte and palatines bear 

 small backwardly-curved teeth. Pectoral and pelvic girdles and 

 limbs are entirely wanting. The small slit-like mouth lies on the 

 lower side of the conical head. The two nares are placed in front on 

 the snout, and near them a blind pit on each side is visible in several 

 genera. These so-called false nares (like the cephalic pits of snakes) 

 lead into canals, which are regarded by Leydigt as sense organs. 



The eyes are always small in correspondence with the subterranean 

 mode of life, and are only visible through the skin as small specks. 

 There is neither tympanic membrane nor tympanic cavity. 



The Gymnophiona live in South America and the East Indies, and 

 feed principally on Worms and Insect-larvee. Joh. Miiller was the 

 first to show that Coscilia ylutinosa possesses, in the larval period, a 

 gill slit on each side, which leads to the internal gills. According to 

 Gervais, Cozcilia compressicauda is born without a trace of branchial 

 apertures, and Peters has recently confirmed this assertion. Peters, 



* Joh. Miiller, " Beitrage zur Anatomie mid Xaturgeschichte der Amphi- 

 hien," Trevirarms ; Zcit.schr.fur PJtys., Tom. IV., 1832. 



E. Wiedcrsheim. ' Die Anatoinie der Gymnophionen." Jena, 1879. 



f Fr. Leydig, " Deber die Sc-bleichlurche (f'cecilia). Ein Beitrag zur anato- 

 mischen Kenntniss der Amphibien," Zcitschr.fii/r irix.?. Znul.. Tom. XVIII. 



