NO. 1788. NORTH AMERICAN EROASILIDM— WILSON. 285 



The one appendage is manifestly the homologue of the other; if we 

 call it a maxilliped in the male, as its position, structure, and function 

 plainly indicate, we must also call it a maxilliped in the female, even 

 though it be degenerate, fused with the head, and considerably 

 changed in form and apparent position. 



Having determined here the names and relation of the several 

 mouth parts, brief diagnoses will be given of them as actually found 

 in the two sexes of a selected type under each of the three sub- 

 families (see pp. 311, 350, and 382). 



The swimming legs. — The first four pairs of swimming legs are 

 biramose in each of the genera. The rami of the first pair vary 

 greatly; in Thersitina and Ergasilus alone are they cylindrical and 

 three jointed like those of the other legs. 



In all the other genera they are flattened into lamellae, obscurely 

 jointed if at all, and with a fringe of large plumose setse around the 

 entire margin. The rami of the second, third, and fourth legs are 

 alike in all the genera, slightly flattened, three or four jointed, and 

 well armed with plumose setee. The fifth legs are uniramose, rudi- 

 mentary, and usually two jointed, with setse only at the tips. A 

 sixth pair of legs is present in most genera upon the genital segment, 

 and are like those found in the same position in the Caligidae, simple 

 knobs, armed with spines or setse. 



The Anal laminse are slender, cylindrical or flattened, and armed 

 with the usual plumose setae, one or more of which are greatly elon- 

 gated, sometimes to half the length of the entire body. 



THE MUSCULAR SYSTEM. 



The Ergasilidae have bodies which are much thickened in propor- 

 tion to their breadth; furthermore, both the ovaries and oviducts are 

 developed inside the cephalothorax. 



Hence these copepods are not as transparent as the Caligidae, and 

 the musculature is usually obscure, especially in the sexually matured 

 female. But in the young of both sexes the body remains flattened 

 and the muscles can be determined with comparative ease. The 

 general arrangement of muscles is very simple as will be seen from 

 figure 1 1 , and their function is the flexion or extension of one part of 

 the body or appendage upon another. 



There are no frontal plates like those in the Caligidae, but there 

 are corresponding flexor muscles. It was suggested under that family 

 that the frontal plates were really the basal joints of the first antennae, 

 fused more or less completely with the frontal margin of the carapace. 



