ANIMAL PARASITES 177 



although of different species. The tawny owl 

 presents by way of contrast (Fig. 116), a parasite 

 that is not slender bodied, but exhibits an alder- 

 manic outline suggestive of unearned increment. 



Fish also have their personal attendants, and 

 one of these, taken from the fresh-water pike, is 

 shown in Fig*. 117 ; this species is also found on 

 carp, and perhaps more often on the small but 

 interesting stickleback. It may seem to be upside 

 down as represented in our illustration, on com- 

 paring it with the other pictures, but its position is 

 correct. The legs are attached to the posterior 

 part of its anatomy, and constitute paddles by 

 means of which the creature can change its 

 host, and depart to pay its attentions to another 

 fish. The two dark spots seen in the forepart 

 of the creature represent the first pair of legs, 

 which have been converted into suckers, by means 

 of which it retains hold of its slippery host. 

 Perhaps, as is the case of the slender parasite 

 of the pigeon, we do this fish-dweller an in- 

 justice by including him with those parasites 

 that live more or less at the expense of their hosts. 

 For there is good reason to believe that he is not 

 a torment to his host, but rather a useful valet. 

 In all probability it derives its nourishment from 

 the superfluous products secreted by the skin of 

 the fish. And when he has satisfactorily arranged 



