OCR Text |
Show 136 CRUSTACEA. matrix. But there is no crustaceous animal known in which thefemale organs of generation are placed at the posterior extremity of the body, and hence we can allow but little weight to this opinion. The ~bservations of Schreffer on the hairs of the feet of these Crustacea, prove that they are so many air tubes; even the surface or the feet of which they are composed, appears to absorb a portion of the air which adheres to it under the form of little bubbles. The Chirocephalua diaphanua, Bened. Prevost, which seems to us to be very closely allied to our BrancMpua palustria, if it be indeed diffet·ent, has, when fit·st hatched, a body divided into nearly equal and almost globular masses. In the first we observe an ocellus, two short antennre, two very large oars ci· liated at the extremity, and two short, slender feet composed offive joints. After the first change of tegument the two com. pound eyes make their appearance, the body is elongated p05• teriorly, and terminated by a conical, articulated tail with two threads at the extremity. The subsequent changes gradually develope the feet, and the oars disappear. The valve-soupapewhich at first extended over and covered the abdomen, diminishes in proportion. The Branchipi are found, and usually in great numbers, in little muddy, fresh water pools, and frequently in those that are formed by heavy rains, particularly in spring and autumn. On the first ap· proach of cold weather they perish. They swim with the greatest fa· cility on their back, and their feet, which they cannot use for walking, while thus employed, present a graceful and undulating motion. This motion creates a current between them, which, following the canal of the thorax, directs to its mouth the atoms which constitute its food; when the animal wishes to advance it strikes the water, right and left, with its tail, which forces it forwards by bounds and leaps. Withdrawn from its element, it moves its tail for a while, and curves itself into a circle. Deprived of a certain degree of humidity, it re· mains motionless. · Benedict Prevost states, that when the male of the species which constitutes the object of his memoir seeks his female, he s"ims round bet·, seizes her by the neck with the two horn-like appendages of his ~earl, and re~a~ns fixed there, until she turns up the posterior extremity uf her tall, m order to approximate the two valves of the copulating organs; this process is analogous to the coitus of the Li· bellulce. The ova are yellowish, spherical at first, and afterwards an· gular; the shell is thick and hard, a circumstance which tends to preserve them. It appears that even desiccation provided it be not c'arried too far, produces no change in the germ, 1 and that the young are hatched as soon as a sufficiency of rain has fallen. M. Desmarest BRANCJUOPODA. 137 r ently remarked Branchipi in the little hollows filled with has requ . . . . ter on the summtt of the rocks at Fonta10ebleau. The fe-raln wa ' d' . f f h I Chirocephalus produces several tstmct sets o eggs, a ter eac mae . 1 d 1 I tl·on at different times, occupymg some lours an even t 1e copu a ' • h le day in the process. Each set consists of from one to four :u:dred eggs; they are ra?idly ejected f;om the fe~ale in. jets of ten or a dozen, and with sufficient force to smk them shghtly m the mud. Benedict Prevost has remarked that the Chir. diapltanua was sub' ect to certain diseases, of which he gives a description. This spe~ ies as we have already stated, does not differ from our Brancltipua pal~tria(l). The two horns, situate~ ~nder the superior _antennre, are composed, in both sexes, of two JOints, the last of which, however, is large and arcuated in the male, and very short and conical in the female. In the Branchipus atagnalia(2), the horns consist of a single joint, and those of the males resemble the mandibles of the Lucanua cervus, in their form, dentations, and direction. Others have no tail; their body terminates almost directly behind the thorax and last feet. Such is the EuLIMENE, Lat. The body of the Eulimenes is almost linear, and has four nearly filiform antennre, two of which are smaller than the others, bearing a great resemblance to palpi, and placed on the anterior extremity of the head. Their head is transverse, with two eyes seated on large and cylindrical peduncles. There are eleven pairs of branchial feet, the three first joints and the last small and tapering; directly after them follows a terminal and nearly semiglobular piece replacing the tail, and from which issues an elongated thread, that, perhaps, is an oviduct. Near the middle of the fifth pair of feet, and of the four following ones, I have remarked a globular body, possibly analogous to the vesicles presented by these organs in the following subgenus. The only species known, Eulimene blanchatre, Lat., Regne Animal, Cuv., III, p. 68; Nouv. Diet. d'Hist. Nat. X, 333; Desmar., Consid. p. 353, 354, is very small; whitish eyes, and (1) Cancer paluiUMus, MUll. Zool. Dan. XL VIII, 1-8; Herbst., XXXV, 3-5; Chirocephalua diapltanua.'J Prev., Journ. de Phys.; Jurin., Monoc., XX-:X..'CII. See Desmar., Consid. LVI, 2-S. This last species is described in the Manuel du Naturaliste of Duchesne under the name of Marleau d'eau douce. (2) Branchiopoda stagnalis, Lat., Hist. des Crust. et des Ins., IV, p. 297; Canttl' atagnalis, L. ; Gammartta stagnalis, F'ab.; .IJ.pua pisciformis, Schaeff',; Gammarus llagnalia, Herbst., XXX, 3-10. Vot. III.-S |