456 THE AMERICAS XATURALIST [Vol. 



are attacked very lightly, while others become heavily 

 parasitized. Doesn't it seem logical to speculate that 

 through intelligent selection and breeding, one could de- 

 velop resistant strains of fish, which would be attacked 

 by so few of the parasitic copepods that the parasites 

 would be almost a negligible quantity? 



These remedies, of course, are not absolute, but they 

 may help a great deal in reducing the loss of the fish. In 

 cases of such parasitism there is no absolute cure known. 

 A most desirable remedy would be one which would de- 

 stroy the adult copepods while they are attached to the 

 structures of the fish, without in any way harming the 

 latter; but all attempts in this^ direction have thus far 

 been without success. The hosts are so delicately consti- 

 tuted that they can withstand only a very slight change in 

 their environmental medium. The adult copepods, on the 

 other hand, can resist powerful chemical solutions by 

 virtue of their resistant body walls. It is obvious that 

 the weak link in the chain of the life-history of these 

 parasites is the free-living period, and in view of this, 

 the real solution seems to be quite clear. One must catch 

 the organisms as they break out of the egg-sacs of the 

 mother and kill them before they come in contact with 

 their hosts. As with a good many of our modern dis- 

 eases, " prevention before parasitism occurs " should be 

 our motto, rather than " cure after parasitism." 



