130 CRUSTACEA. 



rostrum less salient; the valves narrower and less gibbous superiorly, 

 and gaping in front in such a manner as to present a wide and al- 

 most circular opening. The antennae are much larger and have the 

 appearance of being furnished with two horns bent underneath, 

 which are considered by Muller as the organs of generation. Straus 

 could not discover these sexual parts, but he remarks that the little 

 nail terminating the last joint of the two anterior feet — or the second, 

 if we suppose the oars to be the first — is much larger than those in 

 the female, that it has the form of a very large ho6k with a strong 

 outward curvature, and that the seta of the third joint is also much 

 longer; it is by means of these hooks that he seizes the female. The 

 mammillae of the sixth segment of the abdomen are much smaller, and 

 at an early age have the form of tubercles. The inferior antennae 

 excepted, which are longest, the two sexes are nearly alike, and the 

 two valves of their shell terminate in a stylet, dentated beneath, 

 arcuated below, and nearly as long as the valves. Every time the 

 animal changes its tegument, this stylet becomes shorter, so that in 

 the adult it forms a mere obtuse point. 



The males pursue their females with much ardour, and several 

 frequently unite in their advances to the same individual. 



lA. single copulation fecundates the female for several successive 

 gen»irations, and for a period of six months, as ascertained by Jurine. 

 Straus, remarking that the orifices of the ovaries are placed very 

 deeply under the valves and that consequently no part of the body 

 of the male could reach them, suspects that he has no copulating 

 organ, but darts the fecundating fluid under the valves of the female, 

 whence it finds its way to the ovaries; analogy however seems to dis- 

 prove this conjecture(l). Jurine saw them in actu, for a period of 

 eight or ten minutes. The male, first placing himself on the back of 

 the female, seizes her with the long threads of his anterior feet; he 

 then seeks the inferior margin of her shell, and approximating the 

 aperture of his own to that of the latter, he introduces the threads, 

 as well as the hooks of these same feet. He now brings his tail in 

 contact with that of his companion, who at first, refusing to comply, 

 flies with her amorous mate, but finally yields. Little granulated 

 bodies of a green, rose, or brown colour, according to the season, 

 gradually ascend into the matrix and become eggs. Jurine observes, 

 that the males of the D. pulex are but few, when compared to the 

 number of females; that they are extremely rare in spring and sum- 

 mer, but less so in autumn. 



About the eighth day after they are hatched, the young Daphnia 



(1) See Jurine, Hist. desMon. p. 106, et seq. 



