188 MAMMALIA, REPTILIA, ETC. 



boulder stones. These are for the purpose of crushing 

 the shells of the crabs and other crustaceans on which 

 it most delights to feed. It belongs to the usually 

 harmless family of the blennies, one of which, the little 



smooth blenny (Blennius 



Fig. 123. 



pholis), derives its name 

 from a Greek word sig- 

 nifying "slime," on ac- 

 count of the abundant 



The Blenny (Blennius pholis}. t > 



mucus which, in common 



with all fishes, it secretes Irom the medial line of scales, 

 which are perforated to allow the mucus to exude, and 

 thus decrease the friction caused by rapid movements 

 in the water. Many larger fishes support parasites on 

 their scales, and these are usually crustaceans which 

 have undergone a very strange degradation. Of course, 

 they are popularly spoken of as " fish-lice," and have 

 been regarded as unhealthy signs on the part of the 

 fish. Any fishmonger, however, will tell you that the 

 fish thus affected are usually stronger and better than 

 those without them, and Van Beneden has shown that 

 the parasites really live on the excessive mucus, which 

 they thus check and prevent decomposing; so that 

 they are actually serviceable to fishes. The smooth 

 blenny is a good shallow tank object, and may be 

 kept and even tamed there easily, especially if the 

 tank represents the hiding-places of the rock-pools 

 in which it delights when free. The male, like the 

 stickleback, will defend the eggs against enemies. 



