NO. 1404. 



PARASITIC COPEPODS—CALIGIDJ^- WILSON. 



551 



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

 joints of the first antennre, such a homology becomes not merel}^ pos- 

 sible but very complete and sig-nificant. In both families the first 

 antennte 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 ArguJus the prehension is accom- 

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

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

 disk or lunule. 



The second antennfie in Argidvt< are largely tactile, only the ])asal 

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

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



FlG. 50.— APPENDAGES OP THE EARLY CHALIMU.S STAGE SHOWING MODE OF DEVELOPMENT, an^., SECOND 



antenn.e; mxpi. and mxp-., maxillipeds; 1, 2, 3, and 4, swimmini; legs. 



ward. But in Caligus the entire second antenna becomes prehensile 

 (fig. 50, an'.), the basal joint with a stout spine pointing backward, 

 as in Argidvs, 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 antennas as the first pair of foot-jaws, the former without 

 making any comparisons, the latter claiming that they corresponded 

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



The first and second maxillaj develop somewhat toward the close of 

 the chalinuis period, but as thev are rudimentary even in the adult no 

 marked development is ])ossible in the larva. 



