58 NATHAN FASTEN 



clean. Five days later the perch died, but their gills revealed 

 no infection by Lernaeopoda, their death was apparently due 

 to a fungus which had developed on them. The rainbow trout 

 were also found to be free from the copepod. 



Lefevre and Curtis (191 2), in their recent paper on the arti- 

 ficial propagation of fresh water mussels, note a similar prefer- 

 ence on the part of the hookless glochidia of the genus Lampsilis 

 for certain fishes. However, they have found that the glochidia 



v attach themselves to a number of different kinds of fish, 

 although their choice for one is generally predominant. The 

 glochidia are therefore not quite as exclusive in their choice as 

 are the five swimming Lernaeopoda. The reactions observed 

 in the glochidia and in the copepod are, undoubtedly, chemical 

 in nature. In the case of the. copepod there must be something 

 in the blood or other secretions of the brook trout which attracts 

 the parasite to this species of fish. This chemical substance, or 

 substances, must be wanting in the other fish and they are, 

 therefore, not parasitized by Lernaeopoda edwardsii. 



XI. CONCLUSIONS 



From the foregoing discussion it becomes evident that Ler- 

 nacpoda edwardsii is well adapted to its parasitic mode of life. 

 It moves about with a darting spiral motion, thereby cover- 

 ing a maximum of territory with the amount of energy it 

 expends. In many respects this method of locomotion is 

 similar to that of the hunter ciliates. The organism is so 

 strongly attracted by intense light that during the day it fre- 

 quents the upper regions of the water, though it is normally 

 positively geotropic. In this position the copepod is very favor- 

 ably situated, for the brook trout feed near the surface waters 

 throughout most of the day, and hence the parasite is readily 

 accessible to them. At night, on the other hand, the copepods 

 are no longer attracted by light, and since they possess a greater 

 specific gravity than the water, they passively sink to deeper 



:ions. Here, also, their position is advantageous because 

 after sunset the trout frequent the lower strata of water, and 

 they are thus stationed close to the parasites where infection 

 may occur and the life of the copepod thus insured. 



