120 CRUSTACEA. 



hands. To each of the three following segments, is attached a pair 

 effect formed like the two last of the preceding ones. Two of the 

 antennae, superior to the others, are longer, setaceous, simple, and 

 composed of numerous small joints; by their action, they facilitate 

 the motion of their body, and almost perform the office of feet. 

 The inferior — antennales, Jurine~are filiform, usually present but 

 four joints, are sometimes simple, and at others, forked; by the ra- 

 pidity of their motions in the water, they occasion a kind of whirl- 

 pool. In the males, the superior antennae, or one of them only (C. 

 castor) are marked by a strangulation and dilatation, followed by a 

 joint with a hinge. By means of these organs,- they seize their fe- 

 males, in their amorous preludes, either by the posterior feet, or by 

 the extremity of the tail, and keep them, nolens volens, in the pecu- 

 liar position in which they fix themselves. The latter carry off the 

 males, when they are unwilling to gratify their desires on- the" spot. 

 The business of coition is performed, as in the preceding Crustacea, 

 and by prompt and repeated acts. Jurine observed it to occur 

 three times in the space of fifteen minutes. Until the publica- 

 tion of his remarks, it was thought that the male organs of gene- 

 ration were, placed on the superior antennae, and this error appear- 

 ed to be the more probable, inasmuch as an analogous conformation 

 was known to exist in the Araneides. On each side of the! tail, in 

 the female, is an oval sac, filled with eggs — ovaire externa, Jurine — 

 adhering by a very slender pedicle to the second segment, close to 

 its junction Avith the third, where the orifice of the oviduct is also 

 visible. The pellicle, forming these sacs, is a mere continuation of 

 that of the internal ovary. The number of ova they contain aug- 

 ments with age; they are at first brown or dark, afterwards become 

 reddish, and when the young ones are about to be hatched, are al- 

 most transparent, but without increasing in size. If insulated or 

 detached, at least until a certain period, the germ perishes. A 

 single, but indispensable fecundification suffices for several success- 

 ive generations. The same female may spawn ten limes in the 

 space of three months. Allowing it to occur but eight times in that 

 period, and the number of young ones produced to be forty, the sum 

 total of births will amount to near four thousand five hundred mil- 

 lions. The length of time which the young remain in the ovaries, 

 varies from two to ten days, according to the temperature of the 

 season, and various other circumstances. The oviferous sacs 

 sometimes present a greater or less number of elongated glandiform 

 bodies which appear to consist of a collection of Infusoria. 



The young, at birth, have but four feet, and their body is round- 

 ed and without a tail. It was with these that Muller formed his 

 genus Imymone. Some time after — fifteen days, from February to 



