002 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxiin. 



as a sort of sucker, like the luniiles in Caligus. Nothing Hke this has 

 ever been noticed in other species of Lepeophtheirus. 



About half way between this lateral curve and the central incision 

 is a single fiagelliim on either side, which reaches beyond the edge of 

 the transparent border and is evidently sensory. The median sucker 

 on the ventral surface at the base of the frontal filament seems espe- 

 cially well develo])ed in this young form. The remainder of the cara- 

 pace is similar to that of the adult. The free segment is relatively 

 larger than in the adult, lieing three-quarters as long as the genital 

 segment, and at the center, through the bases of the fourth legs, once 

 and a half its width. 



The genital segment is a narrow oblong, only one-fifth as wide as the 

 carapace and two-fifths as long, with parallel sides. At the posterior 

 corners where it joins the abdomen the beginnings of the sexual organs 

 can be plainly seen. On the dorsal surface at either side is the os uteri, 

 or opening of the oviduct to the exterior. This takes the form of a 

 large, broad, and blunt papilla projecting from the angle of the geni- 

 tal segment, on a level with and alongside the dorsal surface of the 

 abdomen. 



Inside the genital segment can be seen the posterior end of the 

 oviduct, coiled irregularly, enlarged somewhat, and easily mistaken 

 for the semen rece])tacles of the male. 



On the ventral surface can be seen the fifth legs as a pair of large 

 and blunt papillae, with tiny setae at their tips. Just in front of 

 these legs a joint can be plainly seen extending across the ventral 

 surface of the genital segment, as though the fifth legs were to be 

 separated from the rest of the segment. This joint also appears 

 indistinctly upon the dorsal surface, but would never be noticed if 

 it were not first discovered on the ventral surface. In front of the 

 fifth legs on the ventral surface may be seen the cement glands, 

 already well formed and with the division of the central lumen into 

 cells plainly visible. In the posterior portion of the abdomen the 

 respiratory muscles extending from the abdomen wall to the cloacal 

 portion of the intestine show that this mode of respiration persists 

 at least for a time after the molt from the chalimus into the adult 

 form. 



Several interesting facts may be learned from this study of the 

 young female. Perhaps the most important one is the necessity for 

 great care in distinguishing between young females and males. The 

 specimens under consideration were judged at first to be males; they 

 were of the right size ; the proportions of the body regions were those 

 of ordinary Lepeophtheirus males, and the coiling of the oviducts 

 at the posterior end of the genital segment looked much like a pair of 

 semen receptacles. But on examining them under high magnifica- 

 tion, in order to explain the curious structures in the genital segment, 



