BRANCHIorODA. 
251 
abdomen and they dart out. Newly laid eggs tVeposited in a glass 
jar, where they were 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 the 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 l)ubbles have entirely disappeared, the 
central one excepted, which contains the alimentary canal under the 
heart; 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 sliorter ; the ros- 
trum less salient ; the valves narrower and less gibbous superiorly, and 
gajjing 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- 
ance 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 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 mammilla; 
of the sixth segment of the abdomen are much smaller, and at an 
early age have the form of tuber’cles. 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. 
A single copvdation fecundates the female for several successive 
generations, and for a period of six months, as ascertained by J urine. 
Straus, remarking that the orifices of the ovaries are placed very 
deeply under the valves and that consequently no part of the body ot 
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 disprove 
this conjecture *. Jurine saw them in actu, for a period of eight or 
See Juriue, Hist, dcs Mon. p. 10t>, ct scq. 
