NO. 1404. 



PARASITIC COPEPODS—CALfaiD.E- WILSON. 



545 



Tlie second antoTina^ and second niaxillipeds retain their prehensil(» 

 function and have changed but little. 



There has been a fusion of the first and a partial fusion of the second 

 thoracic segments of the previous stage with the cephalo-thorax. The 

 third segment has elongated; the rudimentary third legs have devel- 

 oped into a pair quite similar to the 

 tirst and second pairs of the previous 

 stage. Upon the posterior end of 

 this segment appear another pair of 

 rudimentary protuberances which are 

 to develop into the fourth legs. 



The genital segment still remains 

 fused with the abdomen, and the two 

 have increased considerably in size. 



The time has now arrived for the 

 larva to seek its host, and, when once 

 found, it fastens immediately to the 

 host's body. Just how the host is 

 found remains a m3'sterv, but certain 

 facts are self-evident. 



In the tirst place the nauplii and 

 metanauplii swim freely at or very 

 neai" the surface, while the tish which 

 are to serve as their future hostsdo 

 not frequent the surface. None of 

 the surface tish when examined are 

 found infested witii parasites of the 

 genera here considered, with one or 

 two exceptions. And these are forms 

 which are peculiar to the tish on which 

 they occur. 



There is nothing, therefore, in the 

 nature of an intermediate host; tlie 

 larva does not fasten itself upon the 

 lisli which is nearest at hand and re- 

 main until it can seek its proper host. 



It linds in some way at the very tirst 

 the fish it wants and u})on which it is 

 to be found when fully developed. 



Most of the genera here considered 

 infest fish which live at or near the bottom, the Gadida\ Pleuronectida?, 

 etc. And every form of development from the earliest metanauplius 

 stage through to the sexually mature adults may be found upon the 

 same species of fish by careful search at the right season. 



At some time, therefore, dui-iiig tlie two metanauplius stages the 



Fig. 4fi. 



-A YOUNG CH.^I.IMrS 

 R.\P.\X. 



