GENERAL ANATOMY. 15 



shape or other, is always present (PI. LXIV, figs. 7, 

 16; PI. LXV, fig. 11). The third foot of the male in 

 the same genus is sometimes (perhaps not always) con- 

 verted into a clasping organ, the outer branch being 

 bent across the inner and having its last joint armed 

 with several strong spines (PI. LXIV, fig. 20). In the 

 Calanidce and Misophriidce the fifth pair of the male is 

 usually specially adapted as a clasping organ, the limb of 

 one or both sides being reduced to a single branch, and 

 provided with an armature of spines or hooks, which 

 either entirely supersedes the swimming function, as 

 in Temora, or is superadded, as in Centropages; but in 

 other genera belonging to these families the sexual 

 alteration of the limb is not very great (Calanus). 

 Some pelagic genera, which are not represented in the 

 British seas (Euchceta, Undina}, though possessing in 

 the male a strongly developed prehensile fifth foot, 

 have in the female only four pairs of simple swimming- 

 feet. In Undina the male fifth foot is remarkably 

 long and very fantastic in shape, reaching sometimes 

 even beyond the extremity of the caudal segments. 

 The organ may not unfrequently be seen with sperma- 

 tophores adherent to its apex,* and is possibly used as 

 the means of conveying these bodies to the vulva of 

 the female. f It is remarkable, too, that in species so 

 constituted (especially in Undina Darwinii, Lubbock) 

 the spermatophores are very commonly found affixed 

 in a futile manner to the back of the thoracic rings of 



* A similar condition is figured by Dr. Claus in the case of Euchata 

 prestandrece (' Die frei lebenden Copepoden,' pi. xxx, fig. 9). 



f A similar function is performed by tbe maxillary palps (chela?) of 

 male spiders and by the hectocotylised arms of some cuttle-fishes. 



