No. 1401. 



PA RASITIC COPEPODS—CALiniD.E— WILSON. 



545 



The second antennae and second maxillipeds retain their prehensile 

 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 

 first 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 immediate^ to the 

 host's body. Just how the host is 

 found remains a mystery, but certain 

 facts are self-evident. 



In the first place the nauplii and 

 metanauplii swim freely at or very 

 near the surface, while the fish which 

 are to serve as their future hosts do 

 not frequent the surface. None of 

 the surface fish when examined are 

 found infested with parasites of the 

 genera here considered, with one or 

 two exceptions. And these are forms 

 which are peculiar to the fish on which 

 they occur. 



There is nothing, therefore, in the 

 nature of an intermediate host; the 

 larva does not fasten itself upon the 

 fish which is nearest at hand and re- 

 main until it can seek its proper host. 



It finds in some way at the very first 

 the fish it wants and upon 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 Gadidae, Pleuronectidse, 

 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, during the two metanauplius stages the 



Fig. 40.— A yotjng chammus of Caucus 



RAP AX. 



