REPRODUCTION 205 



through three stages : 1, still enclosed within the egg and 

 living on its own yolk ; 2, free within the vitelline mass, which 

 is the product of the other, degenerate eggs and which is 

 directly swallowed by the mouth ; 3, there is no more vitelline 

 mass, but the embryo is possessed of long external gills, 

 which serve for an absorption of nutritive fluid from the 

 maternal uterus, these gills functioning in the same way as the 

 chorionic villi of the mammalian egg. Embryos in the second 

 stage, if artificially released from the uterus, are able to live in 

 water, in the same way as similarly developed larva of S 1 . 

 maculosa. But the uterine gills soon wither and are shed, and 

 are replaced by other gills differing in no respect from those of 

 its congener. And it has recently been ascertained that 

 females of 5. atra from the lower limit of the vertical range of 

 the species occasionally produce their young as larvae and in in- 

 creased number (three or four instead of two), whilst, on the 

 other hand, at high altitudes 5. maculosa may produce young 

 in the perfect condition and few in number. 



There is strong reason to suppose that 5. atra is directly 

 derived from its very close ally ^S\ maculosa ; and in this con- 

 nection it is interesting to observe the complete passage which 

 exists between the two species as regards their mode of gesta- 

 tion, the extremes of which are so very different. 



Spelerpes fuscus, a small Italian salamander, which climbs 

 like a tree-frog, is usually found in limestone caves in which 

 there is no water. It has been ascertained on specimens kept 

 in confinement that the young are born, four in number, in the 

 perfect condition. The development has not been observed, 

 but it is probably similar to that of Salamandra atra. 



Proteus anguinus, the blind perennibranchiate Urodele of the 

 caves on the East coast of the Adriatic, has been observed in 

 some cases to lay eggs, in others to bring forth its young alive. 



III. The Apodal Batrachians 



The burrowing, worm-like, limbless forms which constitute 

 the Order Apoda, the Ccecilians, have long escaped observation 

 so far as their habits are concerned. Their mode of life and 

 their habitat, confined to tropical lands, easily account for the 

 fact that, although close upon fifty species are now described, 

 we are more or less acquainted with the breeding habits of six 



