GYMNOPHIONA. 303 



respect : in Ichthyophis glutinosa (Ceylon) the just hatched 

 young take to the water and lead a larval life of some duration, 

 whereas in Hypogeophis (Seychelles) they are hatched ready for 

 a terrestrial life and there is no larval stage. 



The development has been examined in two oviparous forms, viz. 

 Ichthyophis and Hypogeophis, but has not been fully worked out in any 

 species. The eggs are always laid in holes in the ground and the mother 

 remains coiled roimd them during their development. The segmentation 

 is confined to one pole of the egg, but the layers appear to be formed on the 

 ordinary amphibian type. In Hypogeophis, at least, the blastopore 

 persists as the anus. Three external gills of considerable size are developed, 

 but they vanish before hatching. The eggs increase in size and weight 

 considerably during the developmental period owing either to absorption 

 of water or to the supply of nutriment from the cutaneous glands of the 

 mother. 



In Ichthyophis, in which the breeding season is after the spring monsoon, 

 the eggs become surrounded in the oviduct by a considerable coat of 

 albumen, which becomes twisted in a chalaza-hke manner at opposite 

 poles ; the embryo moreover acquires a number of cutaneous sense-organs 

 on the head and a lateral Une row of similar organs along the body. It 

 also develops a small vertical tail fin and retains a gill-aperture on each 

 side which leads internally to two gill-clefts. The just-hatched larva 

 which is without gills of any kind, either internal or external, makes its 

 way to the nearest water and there lives for a considerable time as an 

 aquatic larva with gill apertures and a tail fin. Eventually these dis- 

 appear, and the animal takes to its terrestrial burrowing hfe. The so- 

 called gill apertures being without gills, the larva has to depend entirely 

 upon its lungs for respiration ; it frequently rises to the surface to breathe. 



In Hypogeophis, which appears to breed all the year roimd, neither 

 lateral line sense-organs nor tail fin are developed, and the gill-clefts are 

 entirely closed at hatching. In this form it has been defuiitely ascer- 

 tained that five visceral clefts are formed in the embryo on each side, viz., 

 a small one (spiracle) between the mandibular and hyoid arch, only 

 developed dorsally, and four others, the last being between the third and 

 fourth branchial arches. 



The Gymnophiona possess a large pronephros which may extend over 

 as many as 12 segments in the larval and embryonic states. 



In the present state of our knowledge there can be no question 

 that the Gymnophiona must be placed with the Amphibia. This 

 is shown by the form of the heart, the presence of a conus 

 arteriosus, the form of the brain and of the urinogenital organs. 

 But they differ from other living Amphibia in the form of the 

 skull, the presence of scales in the dermis, the possession of a 

 large meroblastic egg, the absence of a larva breathing by gills, 

 and the absence in the adult of the carotid arch. 



There are about 40 living species. The group is not known 

 in the fossil state. 



