PARASITISM AND DEGENERATION 



357 



velops in the upper intestine. It feeds on the blood of the 

 you ni;- seal, which finally dies from anaemia. On the sand 

 beaches of the seal islands in Bering Sea there are every year 



thousands of dead seal pups which have been killed by this 

 parasite (Fig. 214). On the rocky rookeries, the young seals 

 are not affected by this parasite. 

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