PARASITIC COPEPODS—CALIGIDyE— WILSOX. 



507 



terminal joint is set into the outer distal corner of the second joint, 

 which is much narrowed at the end for this purpose, and it carries a 

 row of six plumose setre around its maroin. The endopod is never 

 armed with spines, like the exopod, in any species. 



In the third pair of legs the basipods are widened out into a broad 

 lamina, those from either leg meeting- and fusing at the mid line into 

 a single solid apron the entire width of the thoracic area, and often 

 nearly equaling the width of the carapace (fig. 15). This forms a 

 powerful sVimming organ and at the same time assists greatly in pre- 

 hension b}^ closing the posterior edge of the carapace and enabling it 

 to act as a large sucking disk. In addition to these two functions, the 

 lamina is also inclined backward, and being stiff it must make a power- 

 ful prop to assist in the prevention of slipping l)ackward. The exopods 

 and endopods of this pair of legs are very small and are attached to 



Fig. 14.— Second swimming j.eg of adui.t fem.\le Caligcs bonito, ventral surface. 



the outer margin of the basipod laminae, usually some little distance 

 apart. In some species, however, they are so close together as to be 

 almost fused. The endopod is one or two jointed, the basal joint being 

 very short and almost hidden by the edge of the lamina, while the 

 terminal joint is circular. The exopod is two or three jointed, the 

 basal joint armed with a stout claw on its ventral surface, the two 

 terminal joints being the halves of a small ellipse. In some species 

 the two terminal joints are elongated and appressed close to the mar- 

 gin of the basal lamina. Both rami are plentifully supplied with 

 plumose setffi and fringed with fine hairs. 



These first three pairs of legs are connected across the mid line by 

 sternal plates which increase in width from in front backward. 

 Those of the second and third pairs are fringed with hairs along their 

 posterior margins, while in the first legs this margin is smooth. 



