American Fislierief< l^ocichj 99 



Alaska salmon is still varied in character and still to l)e found 

 in all regions of the body. 



Evidently the results of this study stand in sharp contrast 

 with those obtained by Zscliokke and outlined above. They are 

 thus both entirely unexijected and difficult to explain. Since 

 they were secured by the examination of a single series of sal- 

 mon they must, be verified by careful work on the same host in 

 other localities before they can be finally accepted. However, 

 there is another fact which should be borne in mind. The Ahis- 

 ka salmon not only belongs to an entirely different genus from 

 the European but it also has a radically ditt'erent life history in 

 that it perishes after the re])ro<luctive elenu'Uts are discharged 

 and never returns to the oct'an to start u])on another physiologi- 

 cal cycle. (Consequently this ])rominent ])hysiological factor 

 stands in i-adical contrast witb the rejicated migrations of the 

 Atlantic s])ecies and one might reasonably expect to find other 

 radical difi'erenci^s in the biology of the two species. 



It is interesting to note that this limitation of life with a 

 simple reproductive period coupled with the failure of the sal- 

 num to return to the sea is of considerable iulluenee on the bi- 

 ology of the parasites it shelters. As we have already seen, the 

 salmon carries large nundjers of parasites into fresh water and 

 since it does not return they must l)e left there. Among these 

 forms are l)oth adults and larvae. The parasitic life of tlu- fresh 

 water inhabitant does not seem to acquire any eifecti\'e addition 

 from the ])arasites which are introduced in this way siiu'c the 

 examination on many hosts l)oth in and about the lakt's and 

 streams failed to disclose the sabnon ])arasites in any phase of 

 their life history. To be sure some of the eiu-ysted forms may 

 easily reach maturity in the birds or manmuds which feed u|)on 

 the migrating salmon ; yet not only are such instances exception- 

 al but they also ])resent conditions which make it difficult to con- 

 jecture the means by which the adult salmon could be reinfected. 

 It is evident also that the mature ])arasites of the migrating sal- 

 mon discharge their ova into an environment where conditions 

 for further development are hardly present. Even if the em- 

 bryos should complete successfully the first stages in their life 

 history they have no chance to reach the adult salmon which is 

 their final host. A single distome which occurs in the trout of the 



