BRANCHIOPODA. 251 



abdomen and they dart out. Newly laid eggs dcpobited in a glass 

 jar, when; tin v \\viv observed by Straus, were developed in this 

 order. J urine has also furnished us with the result of his analogous 

 observations upon the successive changes in the embryo Daphniae, 

 but made during the winter, and, as the eggs were not hatched till 

 the tenth day, he could consequently detect their developement with 

 more precision. The ovum, on tlie first day, presents a central 

 bubble, surrounded by smaller ones, with coloured molecules in the 

 intervals. These bubbles and molecules appear destined to form the 

 organs by proximating towards the centre, and finally disappear. 

 The form of the foetus begins to be defined on the sixth day ; on the 

 seventh the head and feet are distinguishable ; on the eighth appears 

 the eye as well as the intestine ; on the ninth the network of that eye 

 begins to be visible, and the bubbles have entirely disappeared, the 

 central one excepted, which contains the alimentary canal under the 

 ; t; on the tenth the developement of the foetus is terminated, the 

 young Daphnia issues from the matrix and for a moment remains 

 motionless. 



The males, of those species at least observed by Straus, are very 

 distinct from the female. The head is proportionably shorter ; the ros- 

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

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

 cular opening. The antennae are much larger and have the appear- 

 unee of being furnished with two horns bent underneath, which are 

 considered by Miiller as the organs of generation. Straus could not 

 discover these sexual parts, but he remarks that the little nail termi- 

 nating the last joint of the two anterior feet or the second, if we 

 suppose the oar to be the first is much larger than those in the female, 

 that it has the form of a very large hook with a strong outward cur- 

 vature, 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, 

 nd 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 

 me iv ohtuse point. 



The males pursue their females with much ardour, and several 

 frequently unite in their advances to the same individual. 



A single copulation fecundates the female for several successive 

 generations, and for a period of six months, as ascertained by Jurine. 

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

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

 the inal<' could reach them, suspects that he has no copulating organ, 

 l>ut darts the fecundating lluid under the valves of the female, whence 

 it finds its way to the ovaries ; analogy however seems to disprove 

 this conjecture *. J urine saw them in actu, for a period of eight or 



See Jurinr, Hist, des MOD. p. 106, etteq. 



