SEXUAL DIFFERENCES IX ANTENNAE. 23 



the antenna) of the male, we will find each to be five jointed, and 

 furnished with a most curious variety of spikes and sensory hairs. 

 First there are numerous short stiff spines, next a few much longer 

 ones with a row of regular dots along each margin. Some of these 

 hairs are equal in length to half that of the antenna itself. Of about 

 equal length are three strange much branched slender hairs set 

 around the apex of the terminal joint. Into these hairs, branch 

 nerves can readily be traced. At the apex of the last joint is a claw- 

 like spine. These spines and hairs are very definite in position and 

 number, thus the 1st joint bears 1 short spine, 



the 2nd has 5 spines and 1 long hair, 

 " 3rd " 1 spine and 2 long hairs, 

 " 4th " about 5 spines and 1 long hair, while 

 " 5th " 1 stout claw spine, 2 slender ones, 3 

 branched hairs, 1 long straight hair and a 

 short slight apical thread-like process. 



Between the 4th and 5th joints is a strange hinge arrangement, 

 peculiar to male copepods, and of use in holding on to the female. 

 The antennae of the latter are shorter and less deeply jointed 

 than those of the male; the ratio being as 8 to 11. The 4th and 

 5th joints are practically fused into one, so that the antenna seems 

 to consist of 4 joints only. The spinous hairs are more strongly 

 marked in the female, while the branched and the long hairs are 

 less developed. Apparently then, these being sensory, it falls to 

 the male to search for his mate. In arrangement, the hairs, &c., 

 are much the same in both sexes except that in the female the 

 part that answers to the 4th joint bears 5 spines and 3 long hairs, 

 while what represents the 5th, in addition to having a stout apical 

 claw spine has two others equally well developed and which are 

 equivalent to the two slender spines in the male. It has been 

 said that the claw spine of the male is for use in seizing the 

 female but, seeing that the latter is even better equipped, it seems 

 to me more likely that these are primarily of use in anchoring as 

 parasites to some host. 



The cepalothorax to which the swimming feet are attached, 

 is, in its front part, covered by a great shield, the carapace. On 

 the under side, at the hinder edge of the region thus marked 

 out, is inserted the first pair of feet. Behind the carapace are four 

 distinctly marked off body rings, each bearing in the female a pair 

 of feet on the under side. In the male the fifth pair of feet are 

 suppressed. In structure the first 4 pair of feet are very much 

 alike. The fundamental plan of the typical crustacean foot can be 

 traced clearly. A stout basal part of two stout joints articulating 

 to the body represents the protopodite. To the joint away 



