NO. 2063. NORTH AMERICAN PARASITIC C0PEP0D8— WILSON. 



595 



itself at once to it. It is a general rule that every species of fish has 

 its own peculiar parasites, and hence the latter must have some means 

 of selecting the right host. It is also true that the more fixed the 

 parasite becomes and the less capable it is of moving about, the 

 more exclusively is it confined to one species of fish. 



It is only the free-swimming forms like Argulus and some of the 

 Cahgidae that have a long hst of hosts. Eyesight probably has very 

 Uttle to do with the selection of the particular host, especially in 

 the present family, where the eyes are 

 so rudimentary as to be practically 

 useless. 



Fasten's experiments with Sal- 

 mincola edwardsii, together with re- 

 peated observations by the present 

 author, would indicate that the 

 choice is made by some chemical 

 means, smell or taste, or a combina- 

 tion of the two. Actual attachment 

 is accompUshed by bringing the 



Fig. 15.— First (upper) and second swim- 

 ming LEGS OF COPEPODID LARVA OF ClA- 

 VELLA UNCINATA. 



frontal margin of the head in con- 

 tact with the skin, fin, or giU of the 

 host. The mushroom end of the at- 

 tachment filament then sticks fast, 

 and the filament is withdrawn from 

 the head. In Salmincola, according 

 to Fasten, the larva remains a short 

 time attached by the frontal filament ; 

 in the other genera such an attach- 

 ment has not yet been observed. 

 But in any case this attachment 

 lasts only a short time; the proximal 

 end of the filament is grasped by the 

 second maxiUae and detached from 

 the frontal margin of the head. The maxiUa and filament are then 

 thoroughly fused, and remain as the so-called arms or permanent 

 attachment organs of the adults of this family of parasites. There is 

 always an absorption of the filament, and there may be also an absorp- 

 tion of the maxillae until aU that is left of the original apparatus is 

 the distal mushroom enlargement of the filament, the bulla, buried in 

 the flesh of the host. Many species of Chvella show such a condition, 

 tjie bulla being fastened directly to the ventral surface of the trunk. 

 On the other hand, after the filament has been absorbed the arms 

 sometimes lengthen until they may become two or three times the 

 length of the entire body, as in Lernaeopodina. 



T3ie male does not become permanently attached in this way, but 

 retains his hold on the filament for a short time only and then lets 



