PA RASITK ' ( 'OPEPODS—CA LIGIBM— WILSON. 



551 



possible. But as soon as we recognize in the frontal plates the basal 

 joints of the first antenna?, such a homology becomes not merely pos- 

 sible but very complete and significant. In both families the first 

 antennae are three-jointed, the basal joint being enlarged and modified 

 to serve a prehensile function, while the two terminal joints are much 

 smaller and wholly tactile. In Argul/us the prehension is accom- 

 plished by means of a stout hook developed at the distal end of the 

 basal joint, while in Oaligus the same result is attained by a sucking 

 disk or lnnule. 



The second antennas in Argulus are largely tactile, only the basal 

 joints being prehensile in function, and even these have nothing but 

 stout spines to assist in preventing the copepod from slipping back- 



PiG. 60.— Appendages of the early chalimus stage showing mode of development, an 2 ., second 

 antknn.k; mxp 1 . and mxp 2 ., maxillipeds; 1, 2, 3, and 4, swimming legs. 



ward. But in Caligys the entire second antenna becomes prehensile 

 (tig. 50, an 2 .), the basal joint with a stout spine pointing backward, 

 as in Argu! us, while the terminal joint is developed during the chali- 

 mus period into a strong sickle-shaped claw, operated by powerful 

 muscles, and fully capable of rendering material assistance to the 

 maxillipeds in piercing the skin of the host and obtaining a firm hold. 



Both Baird (1850) and Pickering and Dana (1838) described these 

 second antennae as the first pair of foot-jaws, the former without 

 making any comparisons, the latter claiming that they corresponded 

 to the second maxillae in decapod Crustacea, a manifest error. 



The first and second maxillae develop somewhat toward the close of 

 the chalimus period, but as they arc rudimentary even in the adult no 

 marked development is possible in the larva. 



