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Show 166 ARACHNIDES. diastole of the heart. Both . sexes frequently eject from the anus an excrementitious fluid, part of which is milk-white, and the remainder black a ink. The nervous system is composed of a double cord occupy-ing the median line of the body, and of gang lions which distribute nerves to the various organs. M. Dufour has not been able to determine the number and disposition of these gang· lions but from the figure of this system given by TreviranusV cb~r deninnern, bau des Arachniden, tab. V, fig. 45-thcre are but two. The observations of the latter will also supply the want of those relative to the organ of the circulation by · M. Dufour, which, according to him, appears to consist of a simple dorsal vessel, as well as ~ith resp~ct to the testes and spermatic vessels, on which he Is totally sllent. The dorsal region of the abdomen in several Araneides, those especially which are glabrous or but slightly pilose, ex· hibits depressed points varying both in number and arrange. ment. M. Dufour has ascertained that these little orbicular depressions are caused by the insertion of filiform muscles, which traverse the liver, and which he has also observed in the Scorpions. 'I'hc one or two pairs of pulmonary sacs are indicated exter. nally by as many yellowish or whitish spots near the ventral base, and immediately after the segment which by means of a fleshy thread unites the abdomen with the thorax. Each pulmonary bursa is formed by the superposition of numerous, triangular, white, and extremely thin leaflets, which become confluent round the stigmata, and whose number exactly equals that of the pulmonary sacs. When there are four, a sort of fold or annular vestige found even in those where there are but two, and placed directly behind them, forms a line that separates the two pairs. The females have two very distinct ovaries, lodged in a spe· cies of capsule formed by the liver. In an unfecundated state they appear to be composed of a spongy, flaky kind of tissue, formed by the agglomeration of rounded, and scarcely visible corpuscles, which are the germs of eggs. As the results of PULMON A RilE. 167 fecundation become more apparent, the cluster formed by these ova(l) becomes less compact, and they are seen to be laterally inserted on several canals. Their great analogy to the ovaries of the Scorpions induces the same observer to presume that they form meshes terminating in two distinct oviducts, which open into a common vulva. The figure of the latter varies; sometimes it is a longitudinal bilabiated slit, as in the Micrommata argelasia; sometimes it is protected by an elongated operculum with a caudiform termination, as in the Epeira diadema; and at others resembles a tubercle. With respect to the simple eyes, or ocelli, he remarks, that they shine in darkness like those of Cats, and that the Araneides most probably enjoy the faculty both of nocturnal and diurnal vision. The abdomen becomes so putrid and decomposed after death, that its colours and even its form are soon destroyed. M. Dufour, by means of a rapid desiccation, the mode of which he points out, has succeeded in remedying this evil to a great degree. The silk, according to Reaumur, is first elaborated in two little reservoirs, shaped like tears of glass, placed obliquely, one on each side, at the base of six other reservoirs, resembling intestines, situated close to each other, flexed six or seven times, proceeding from a little beneath the origin of the abdomen, and terminating in the papillre by a very slender thread. It is in these last mentioned vessels th3:t the silk acquires a greater degree of firmness and other properties peculiar to it; they communicate with the preceding ones by branches, forming a number of geniculate turns, and then various pieces of net-work(2). The newly spun filaments, when first drawn from the mammillro, are adhesive, and a ce,rtain degree of desiccation or evaporation is required to fit them for their destined purposes. When the temperature is propitious, (1) For their development and that of the fretusJ see the admirable work of H~rold. (2) See Treviranus, on the same subject. |
