OCR Text |
Show 154 CRUST ACF.A. NicOTHOE, Aud. and Edw. These animals terminate the Crustacea, and are distinguished fr • • i' om all others of that class by their hcterochtical •orm. To the naked eye they seem nothing more than two lobes united in the form of horse-shoe, which enclose two others. By the aid of glasses, how~ ever, we discover that the two large lobes are formed by the gre t expansion of the sides of the thorax, which resemble wings a • ' a~ almost oval and thrown behmd; that the two others are extern . f a1 ovaries or clusters o eggs, analogous to those of a female Cyclo and inserted, one on each side, into the base of the abdomen p~, means of a short pedic1e; and that the body of the animal is co:. posed of the following parts: 1, a distinct head furnished with two separate eyes; two short, setaceous, lateral antennre formed of el • ven joints, each with a hair on the inner side; a mouth forming e circular aperture which acts a3 a cup, and accompanied on each s'da . h . fi I e w1t -anterior eet-maxilliform appendages; 2, a thorax of fo segment~, W'ith fi ve pau· ·s o f feet beneath, the two anterior of whicuhr are termmated by a stout hook, and are b'identated on the inner sid. the remaining eight being formed of one large joint, terminated:' two nearly equal and cylindrical stems, each composed of th y · · d l'. • • ree JOints, an turmshed w1th .setre: 3, a ~o~nted abdomen of five annuli, the first and largest of which giVes or1gm to the oviferous sacs· th Iast '1 s termm· ate db y two long hairs. The lateral expansion me'reely appears to be an e:c-c~ssive development of the fourth and last ring of t.he thorax. W1thm we may perceive two kinds of entrails origi· natmg from. t?e. median li~e of the body, which may be considered as creca or divi~lons of the m~estinal ~anal in a state of hernia. They are endowed with a very dectded pens tal tic motion. We have seen t• hat the •s tomach of. the Arguli also exhibits two c".."..." ca , w h'I C h ram1· ry m th.e wmgs of t~eir shell, and it is possible that these thoracic ex· panswns .of the N Icothoes may be two analogous Jobes( 1 ). Nzcothoe astaci, Aud. and Edw. Ann. des Sc. Nat., 1826, XLIX, 1, 9. The only species known; it is about half a line lo~g and three lines broad, the thoracic enlargement included. It IS rose-coloured, paler on the oviferous sacs· the expansions yellowish. It adheres closely to the branchire' of the Lobster, ~nd penetrates deeply between the filaments of those organs. It Is on)~ found in small numbers, and on a few individuals. All tl~e Nicothoes observed by these two naturalists were furnished With ovaries; it is probable that previously to fixing themselves tl) In this case ' the genus may b c approx1. mated to the precedm. g one. PlEClLOPODA. 155 on tbe branchire of the Lobster, and before their thoracic lobes have acquired their ordinary development, they can swim; that development, as is the case with the body of the Ixodes, . may be the result of superabundant nutrition. TRILOBITES. According to Brongniart and various other naturalists, it is in the vicinity of the Limuli and other Entomostraca with numerous feet, that we should place these singular fossil animals, originally confounded under the common name of Entomolithus paradoxus, and now designated by that of Trilobites, of which an excellent monograph, enriched with good lithographic figures, has been published by that gentleman(!). By this hypothesis we have to admit as a positive or at least highly probable fact, the existence of locomotive organs, although, notwithstanding the most careful investigation, no vestige of them has been discovered(2). Presuming, on the contrary, that these animals were deprived of them, I thought that their natural position was in the neighbourhood of the Chitones, or rather that they constituted the original stock of the Articulata, being connected on the one hand with these latter Mollusca, and on the other with those first mentioned, and even with the Glomeres(3), to which some Trilobites, (ll M. Eudes Deslongchamps, professor of the University of Caen, Count Raaoumowski, M. Dalman and other savans have since published new observations on these fossils. M. Victor Audouin, zealously advocating the opinion of Brong· niart, has contested that published by me, in which I approximate them to Chiton. The great difficulty was to prove the existence of feet, and this he has not done. The application of his theory of the thorax of Insecta to the Trilobites, appears to me so much the more doubtful, as, according to my view of the matter, the first annuli of the abdomen of Insects alone represent the thorax of the Crustacea De· capoda. (2) M. Parkinson (Outlines of Oryctolo&Y) thinks he has perceived them, ud auapetts that they are unguiculated. See also the EntorrwatrtUit~ granulewe Brongn., Trilob., III, 6, Ann. des Sc. Nat. tome XV. (3) Firat edition of the Regne Animal, tome In, p. 150, 151. There is no Branchiopoda known which can contract itself into the form of a ball. This character is peculiar to Typhis, Sphzroma, Tylos, and Armadillo among the Crustacea; and among the class of apterous Insects to Glomeris, a genua which is at the |