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crustacese entomostraca and their allies formed in many 

 cases the principal basis of the food of fish. Now it so 

 happened that it was these small creatures, when swal- 

 lowed, performed a function quite apart from that of the 

 nutrition of the fish which swallowed them. There was, he 

 took it, not a single marine or fresh-water crustacean of 

 small size which was not liable itself to entertain or har- 

 bour parasites, which must occur in innumerable quantities ; 

 but it so happened that all the known parasites, of which 

 there were many thousands, which were obtained from the 

 bodies of fish, gained their entrance to the said fish through 

 food, and that this food was, in nine cases out of ten, if 

 not in ninety-nine out of one hundred, small animals. So 

 curious was this subject, that one single statement of the 

 results of experiment would prove its interest much more 

 than any attempt to grasp a subject of such infinite 

 intricacy. 



Professor LEICHEART was anxious to find the cause of 

 parasitism in the salmonidae. They had in the salmon and 

 trout family a group of parasites with the queer name of 

 Echinorhynchi. By experimenting with gameri, he had 

 actually succeeded in rearing with gameri in tanks, in an 

 aquarium, the eggs of parasites which had come from the 

 trout. He had fed these crustaceans with the germs which 

 had come from the salmon and trout family, to such an 

 extent that they actually succumbed from over-infection. 

 There was here, therefore, an instance throwing a clear 

 light on the means of infection of those fishes which formed 

 that family. Now, what obtained in that case obtained in 

 myriads of others, and it would be his business in the 

 communication he had shortly to read, to set forth, in more 

 clear and emphatic terms than he was able to do in those 

 cursory observations, data on which the importance of this 



