THE FISHES, MOLLUSCA, AND OTHEK OBJECTS. 27 



them is to obtain a portion of the eel's skin, from 

 the belly, when the scales may there be observed in 

 their natural position. 



To omit notice of those common fishes, the Stickle- 

 backs, would show how little the habits of these 

 freaky creatures had been observed by us. Yarrell 

 enumerates seven species as decidedly British. 



Fig. 15. 



Scale of Grayling (Thymallus vulgan's). 



Strange to say, many of these are purely marine 

 in their habits, thus indicating a degree of special- 

 isation, or adaptation to varying circumstances, on 

 the part of the genus, which may have been the result 

 of physical geological changes. Others, such as the 

 Kough-tailed Stickleback (Gasterosteus aculeatus) live 

 both in fresh and salt water, and so far connect the 



