116 REPTILIAN WATER TRESPASSERS. 



them while the reptile is beneath the water, but can 

 be opened for the purpose of respiration when at the 

 surface. 



The second point in the economy of a water tres- 

 passer, is the manner of progression. It has already 

 been mentioned that all snakes can propel themselves 

 through the water by an undulating movement of the 

 body. Those species, however, which almost exclu- 

 sively inhabit the water, have their structure modified 

 so as to suit their way of life. The tail portion of the 

 body, instead of being round, like that of the land 

 snake, is widened and flattened; assuming, in fact, 

 almost the exact shape of the eel's tail. 



There are many species of water snakes, more than 

 seventy species being in the collection of the British 

 Museum. Some of them, among which is the species 

 which has just been mentioned, are such thorough 

 trespassers on the sea that not only cannot they live 

 upon land, but they soon perish in fresh water. Occa- 

 sionally, when there has been a severe storm, they are 

 thrown ashore, where they very soon die. Sometimes 

 they are driven up the mouth of tidal rivers, but, 

 unless they can make their way to the sea, they do not 

 long survive the change of element. 



They are among the venomous Serpents, and are 

 held in great dread by the fishermen, in whose nets 

 they are often accidentally taken. 



As is the case with many fishes of the warmer seas, 

 the colours of these water snakes, though brilliant 

 during life, are fugitive after death, and often vanish 

 entirely from the stuffed skin. It is a curious fact that 

 even during life the colours are brightest in the young 



