CONFERENCE ON THURSDAY, JULY 12, 1883. 



Professor HUXLEY, P.R.S., in the Chair. 



THE DESTRUCTION OF FISH AND 

 OTHER AQUATIC ANIMALS BY IN- 

 TERNAL PARASITES. 



THIS communication is not intended to be an exhaustive 

 memoir. The subject is a wide one, yet it may with truth 

 be said that few persons are aware of its importance. 

 As regards man and the higher animals, physicians and 

 other professional persons have a direct interest in con- 

 ducting researches amongst the parasites ; nevertheless, it 

 is surprising to what an extent mere prejudice has 

 operated to prevent labourers from entering into this 

 instructive field of comparative pathology. 



Taking a comprehensive grasp of the study of parasites 

 it will be readily admitted that the extent of the subject 

 is in itself rather appalling. If you consider that for every 

 known species of bird, beast, reptile, and fish, acting as 

 "hosts," there are probably, on the average, not less than 

 four times as many different species of " guests " liable to 

 occupy their bodies, you will then gain some adequate 

 notion of the zoological difficulties of the study. If, further, 

 you will consider that by far the larger proportion of all 

 these parasites undergo transformations, often of a complex 



