BRANCHfOPODA. 243 



the anterior pair, corresponding to the second jaws, differs slightly 

 from those that follow. Jurine compares it to a kind of hands. To 

 eacli of tin* throe following segments is attached a pair of feet formed 

 like the last of the preceding ones. Two of the antennae, superior 

 to the others, are longer, setaceous, simple, and composed of nu- 

 merous 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 rapidity of their 

 motions in the water, they occasion a kind of whirlpool. In the males, 

 the superior antennae or one of them only (C. castor) are marked by a 

 ^illation and dilatation, followed by a joint with a hinge. By means 

 of these organs, they seize their females, in theiramorouspreludes,either 

 by the posterior feet, or by the extremity of the tail, and keep them, no- 

 lens volens, in the peculiar position in which they fix themselves. The 

 hitter carry off the males, when they arc 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 observ- 

 ed it to occur three times in the space of fifteen minutes. Until the pub- 

 lication of his remarks, it was thought that the male organs of genera- 

 ion were placed on the superior antennae, and this error appeared 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 externe, Jurine ad- 

 hering by a very slender pedicle to the second segment, close to its 

 junction with 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 augments with 

 age ; they are at first brown or dark, afterwards become reddish, and, 

 when the young ones are about to be hatched, are almost transparent, 

 but without increasing in size. If insulated or detached, at least 

 until a certain period, the germ perishes. A single, but indispensa- 

 able fecundification suffices for several successive generations. The 

 same female may spawn ten times in the space of three months. Al- 

 lowing 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 millions. 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 circum- 

 stances. The oviferous sacs sometimes present a greater or less 

 numher of elongated glandiform bodies which appear to consist of a 

 collection of Infusoria. 



The young, at birth, have four feet, and their body is rounded and 

 without a tail. It was with these that Miiller formed his genus 

 Amymone. Some time after fifteen days, from February to March 

 they acquire another pair of feet, constituting the genus Nauplius, 

 Miiller. After the first change they have the form and all the parts 

 which characterize the adult animal, but more exiguously propor- 

 tioned; their antennae and feet are proportionally shorter. After 

 thrice changing their skin they arc capable of propagation. Most of 

 these Entomostraca swim on their back, dart about with great 



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