REPTILES 



443 



water, looking very much like a minute eel. After a somewhat 

 prolonged aquatic existence the young Csecilian loses its tail-fin, 

 the gill-clefts close up, and other changes in structure take place. 

 It then leaves the water, and spends the rest of its life as a 

 burrowing terrestrial animal. 



In certain Csecilians which inhabit the Seychelles Islands 

 (species of Hypogeophis) the free-living tadpole stage is eliminated 

 from the life-history, as in some of the tailless Amphibians already 

 described (see p. 440). As before, the female protects her eggs 

 by coiling round them, and a tadpole stage is passed through 



Fig. 967. — Development of a Caecilian {Ichthyophis glutinosa) 



A, Female coiled round her eggs, reduced ; b, bunch of eggs ; c, an egg, enlarged, showing investing membrane 

 and supporting strings ; D, an advanced embryo, with external gills and remains of yolk-sac, enlarged. 



before hatching, in which external gills and four pairs of gill-clefts 

 are present, but no tail-fin. When the young animal leaves the 

 egg it resembles the adult in appearance, for the gills have dis- 

 appeared and the gill-clefts closed up. It at once takes to the 

 burrowing mode of life. 



In a large Csecilian {Typhlonectes compressicaudatd) which 

 inhabits the northern part of South America, development is 

 entirely internal, and the young when born closely resemble their 

 parents. A tadpole stage with reduced gills is passed through 

 before birth, but, so far as we know, this species spends the whole 

 of its life burrowing in the ground. 



LIFE-HISTORIES, &c., OF REPTILES (Reptilia) 



In the higher Vertebrates, including Reptiles, Birds, and 

 Mammals, development is always direct, there being no larval 

 form, though the young are sometimes in a rather embryonic 

 state when they first make their appearance in the world. 



