no.1404. PARASITIC COPEPODS—CALIGIDjE— WILSON. 505 



may act as a support or crutch on which to raise the body of the 

 parasite high enough from its host to render the use of the .swimming 

 feci and mouth organs possible. But there are several considerations 

 which render such a function quite improbable, in the first place 

 the parasite uses its feet when on its host simply to keep the water 

 beneath the carapace agitated for purposes of respiration; and there 

 is space enough for this, ordinarily, without raising the carapace at 

 all. Again, the raising of the carapace and balancing it upon this 

 fork would weaken the parasite's hold enough to render any sudden 

 or unlooked for friction dangerous. And then, if the fork were 

 to function as a support there would certainly be need of some mus- 

 cular arrangement to adjust, hold, and remove it, as occasion 

 demanded; but there are no such muscles in connection with this fork, 

 and, so far as can be determined, no means of adjustment whatever. 



And, finally, there would be very little demand for such a support, 

 because when the terminal claws of the second maxillipeds are driven 

 into the skin of the host the parasite's body is ordinarily raised to a 

 greater distance than the length of the sternal fork, and by straighten- 

 ing the basal joints of the same appendages it can be raised still farther 

 without in the least loosening its hold. 



A. Scott, in the memoir already referred to, writes that the function 

 of the furca is unknown. But it seems at least possible that it may 

 be used for the purpose already suggested, to prevent any slipping 

 backward upon the host when the parasite has loosened its claws and 

 is moving about over the host's bod}\ 



It would thus correspond in function as well as position with the 

 papi Hated area and the spines upon the basal joints of the second 

 maxillipeds in the Argulidse. Its position between the bases of the 

 second maxillipeds, its backward inclination, and the entire absence of 

 spines or papillated areas upon the maxillipeds themselves give at 

 least a probability to this view. 



Of the swimming legs the first and fourth pairs are uniramose in 

 nearly all the genera while the remaining pairs are biramose. The 

 genus Alrltion has the legs all biramose, but the fourth pair are rudi- 

 mentary. As will be seen from the key there are several other genera 

 not represented in North American waters which have all four 'pairs 

 biramose like Alebion, while ( 'alistes and Luetkenia have the tirst pair 

 only uniramose, the other three being biramose. 



In the firs! pair the basipod is simple and considerably larger than 

 the terminal joints, except in Caligodes, where it is the same size. It 

 frequently carries upon its posterior ventral surface one or two spines 

 whose bases are enlarged and which are inclined backward (tig. 13). 

 The exopod is well developed, 1 wo-jointed and in line with the basipod. 

 The terminal joint is often appropriately called the ** hand" on account 

 of its shape. 



