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Show 120 CIWSTACEA. hands. To each of the three following segments, is attached a pair ~r feet formed like the two last of the preceding ones. Two of the antennre, superior to the other·s, 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 rapidity of their motions in the water, they occasion a kind of whirlpool. In the males, the superior antennre, or one of them only (C. caator) are marked by a strangulation and dilatation. followed by a , joint with a hinge. By means of these organs, they seize their females, in t?eir amoro~s preludes, either by the posterior feet, or by the extremity of the tall, 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 publication of his remarks, it was thought that the male organs of generation were placed on the superior antennre, 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 fe~ale, is an oval sac, filled with eggs-ovaire externe, Juri;e~ dh.erm~ by a. very slen~er pedic1e to the second segment, close to lts JUnctiOn with the third, where the orifice of the oviduct is als visible. The pellicle, forming these sacs, is a mere continuation 0~ that of ~he internal ovary. The number of ova they contain augmen~ s wtth age; they are at first brown or dark, afterwards become redchsh, and when the yo.ung ones are about to be hatched, are almost transparent, but wlthout increasing in size. If insulated or d_etached, ~t ~east until a certain period, the germ perishes. A ~mgle, but mc.hspensable fecundification suffices for several successIVe generations. The same female may spawn ten times in the spa~e 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 t~tal of r births will amount to near four thousand five hun~red mil· ho~s. fhe length of time which the young remain in the ovaries, var~es from two. to ten days, according to the temperature of the season., and variOus other circumstances• The OV·I~t erous sacs so~ettme~ present a greater or less number of elongated glandiform bo~Ies which appe~r to consist of a collection of Infusoria. he yo.ung, at brrth, have but four feet, and their body is round· ed and without a tail · It was · h h wit t ese that Muller formed his genus .9.mymone. Some time after--fifteen days, from February to BBANCHIOPODA. 121 March-they acquire another pail· of feet, constituting the genus Naupliu8, Muller. After the first change they have the form and all the parts which characterize the adult animal, but more exiguously ro ortioned; their antennre and feet are proportionally shorter. ~ft~r thrice changing their skin they are capable of propagation. :Most of these Entomostraca swim on their back, dart about with great vivacity, and move both backwards and forwards with equal facility. For want of animal substances they will attack vegetable matters, but the fluid in which they live does not pass into their stomach. The alimentary canal extends from one extremity of the body to the other. The heart in the C. castor is oval, and situated under the second and third segment of the body; a vessel is given off ateach of its extremities, one running to the head, and the other to the tail. Directly under it is a second analogous, but pyriform organ, which also pr·oduces a vessel at each end, corresponding pet·haps to the branchio-cardiac canals, mentioned in our observations on the circulation of the Crustacea Decapoda. From several experiments made by Jurine upon various Cyclopes, alternately asphyxiated and resuscitated, it would appear that in this sort of resurrection the extremity of the intestinal canal gives the fit·st signs of life, and that the irritability of the heart is less energetic; that of the antenure, in the males especially, of the palpi, and lastly of the feet. is inferio1·. No alteration is effected in the antennre by amputating a portion of them; the reintegration takes place under the skin, for the organs reappear in all their entit·eness at the ensuing moult. The 0. staphylinus, from its shorter antennre, the superior of which consist of a considerably less number of joints than those of other Cyclopes, while the inferior, on the contt·ary, have mot·e; and from the shape of its body which gradually diminishes towards its posterior extremity, so that it seems to have no tail or at least none that is abruptly formed, and its back, in the females, being armed with a kind of horn posteriol'ly arcuated, forms a particular division. The G. castor, and some others whose inferiot· antennre and mandibular palpi are divided above their base into two branches, may also compose another group. The one designated by Leach under the generic name of Calanus, might in fact constitute a separate subgenus, if it were true that the animal on which it is founded had no inferior antennre; but has that gentleman satisfied himself that such is the fact, by personal observation, or does he depend upon the assertion of Muller? 0. quadricornis; Monoculus quadricornis, L.; Mull., Entom., XVIII, 1-14; Jurine, Monoc., I, II, III. All the antennre simple or undivided; the inferiqr with four joints, and theil· length VOL, IIJ.---Q |