NO. L-s-za. I'ARAtilTIC COPEPODS— WILSON. 327 



We have already stated that the females remain throughout life 

 fixed ill one position upon their host. This is true of all the genera 

 belonging to the subfamily a".:<:l constitutes a fourth step in degener- 

 ation as well marked as the three which have preceded it." 



The last three of these steps, however, and a part of the first one, 

 have been confined to the female, while the male has escaped their 

 influence. 



As a result we find in the present subfamily the greatest sexual 

 dissimilarity in the entire family of the Caligidi©. 



Indeed, the two sexes of every genus in the PandarinjB are so unlike 

 that the males have been considered a separate genus from the 

 females. And not only so, but the males of all the genera have been 

 made congeneric, and grouped together under the single genus '' No- 

 gagus.'^ Furthermore, this male "genus" has been ]:)laced by the 

 great majority of writers in the subfamily Caligin?e rather than in 

 the Pandarina?, where the females all belong. This will be more fidly 

 discussed under the genus name Nogaus (see p. 439). It serves here 

 simply to emphasize the sexual difi^erences, and to make it evident 

 that in considering their ecology as well as their morphology most 

 if not all of the statements must be understood as confined to a single 

 sex. The first step in degeneration, as already noted under the Cali- 

 ginse, was the mechanical hindrance afl'orded by the egg strings, and 

 the strong incentives for remaining on the body of the host. Of 

 course the latter was the only one operating upon the male, and it 

 did not exert much influence so long as the female retained the power 

 of free swimming. 



As, however, this power gradually weakened in the Caligiiiie and 

 still more in the Euryphorinse, the incentive for the male to remain 

 upon the host with the female became stronger. 



And here in the Pandarina?, where the female has become a fixed 

 form and correspondingly degenerate, the incentive operates with 

 its full power on the male, and we find him in the same condition as 

 were the females of Lepeoj^htheirus and other Caligids, that is, capable 

 of swimming freely but under ordinary conditions remaining upon 

 the same fish, along with the female, during his entire life. Wliile 

 the male has thus resisted the degenerative influences so much 

 longer than the female, yet when he once yields the transition is 

 more rapid, and in the very next subfamily, the Cecropinae (see p 465), 

 we find the male degenerated into a fixed form exactly like that 

 of the female. 



a The three previous steps are: (1) The mechanical hindrance afforded by the egg 

 strings and the lack of incentive to free swimming; (2) the loss of the lunules on 

 the frontal plates, and the consequent restriction of the free scuttling motion; (3) the 

 development of dorsal plates on the thorax segments, thereby diminishing the freedom 

 of bodily movement. 



