NO. 1404. PARASITIC COPEPODS—CALIQIDJE— WILSON. 485 



Sucli a change in habits, constituting as it does a long step toward 

 that tixedness of position wliich precedes radical degeneration, ninst 

 have some adequate cause. These three genera have practically the 

 same swimming apparatus as Odllgiis^ and if it is never used there 

 nuist be some preventive influence whicii operates in their case but not 

 in that of CuliguH. 



In the author's o])inion this influence may be found in the presence 

 of sucking disks on the frontal plates of CuVkjiix and their entire 

 a])sence in the other genera. Their presence gives to Caligiis Ww 

 same scuttling motion as Argnhtx detains from its first maxillipeds. 

 In this way they move about over the surface of their hosts with great 

 rapidity and upon the slightest provocation. But the other g(mera, 

 lacking the sucking disks, are dependent upon thc^ second antenna^ and 

 the maxillipeds for locomotion over the surfac(\ and can not conse- 

 quently move al)out with any rapidity. For this I'eason they do not 

 change their position as oft(Mi as (hHyus but r«Mnain a long time fixed 

 in one place. Indeed, when an attempt is made to remove them from 

 their host, only the males and inunature females move about in order 

 to est'ape. The mature females usually settle down tii i<!t(( and oidy 

 cling the more tightly. When removed fi'om their hosts and pi ;ced in 

 aijuaria thes(> g(>nera settle u[X)n the bottom or sides and remain sta- 

 tionar}" for long periods, in marked contrast to the restless ju-tivity of 

 Ctiligus. This fixity of position can not help reacting unfavorably 

 U])on any tendency toward free swinmiing which might still be 

 retained by the copepod. 



To recapitulate, then, we find that none of the Argulidro exhibit 

 degeneration or even any tendency toward it. They have all retained 

 completely both the ability and the inclination to swim freel}' and to 

 move about over the body of their host. 



Among the Caligina^ the genus (JtilUjuH possesses even more ability 

 than ArguhiK^ and the males and immature females retain pi'actically 

 the same incentives. " But for the mature females every influence oper- 

 ates toward remaining upon their host, and they are very seldom cap- 

 tured swimming freely. All the species of CallguK.^ however, still 

 move about over their host's body upon the slightest provocation. 

 Other genera, l)eing destitute of lunules, lack the ability to move 

 al)out on the body of their host with any freedom. 



This acts as a still stronger damper upon their movements, and 

 although the\' retain fully the ability to swim they almost never exer- 

 cise it. They not only remain upon one host all their lives, but thev 

 also fasten themselves in a single spot and stay there continuously. 

 They thus exhibit the initial stages of degeneration, whose next step 

 is to l)e a partial loss of the ability left unused. 



While speaking of locxmiotion mention nuist be made of a pernicious 

 habit common to many of the Caliginie. This consists in crawling up 



