244 SNAKES. 



land snakes. Thus we have links between sea and land 

 snakes, between fresh water and salt, and between these latter 

 and fishes, for in many instances the affinities are so close 

 that naturalists have doubted in w4iich class to place them. 

 When that remarkable animal, the Lepidosiren, w'hich Darwin 

 calls a living fossil, was first brought from Africa some thirty 

 years ago, it was found to present so many characteristics 

 in common with both reptiles and fishes, that it was for 

 some time a mooted question in which class to place it. In 

 appearance it more resembles the former, with its four curious 

 filamentary limbs, which Owen considers ' the beginnings of 

 organs which attain full functional development in the higher 

 vertebrates.' The same high authority has decided that the 

 only character which absolutely distinguishes fishes from 

 reptiles, so closely are some of them allied, is whether or not 

 there is an open passage from the nostrils to the mouth; and 

 the ' Lepidosiren ' is now known as ' the mud-fish of the 

 Gambia/ the ichthyic characters predominating. 



Sea snakes were not unknown to the ancients. Aristotle 

 mentions them (Taylor's Translation, 1812, Book ii. vol. 6), 

 * Of sanguineous animals, however, there remains the genus 

 of serpents. But they partake of the nature both of terres- 

 trial and aquatic animals. For most of them are terrestrial, 

 and not a few are aquatic, and which live in potable water. 

 There are also marine serpents similar in form to the terres- 

 trial genus, except that their head more resembles that of a 

 conger. There are, however, many genera of marine ser- 

 pents, and they are an all-various colour ; but they are not 

 generated in very deep places.' 



These latter words suggest what has not been mentioned 



