Of the female generative system.—It has been long known that the orifices of the gene rative organs in female spiders are situated at the base of the abdomen. We observe on that part of the body two distinct cavities, (fig.103, a, a,) which are closed by opercular pieces of derable difference among authors with respect to this subject ; it therefore requires farther ex amination. Treviranus and Leon Dufour have described these organs as consisting of three elongated tubes ; of these, two are lateral and mutually communicate at their apices, the third is mesial and communicates with the lateral by three branches which we observe on either side. All of them, lastly, terminate at the vaginal orifice which is concealed by a more or less rounded plate, and is situated on the middle line of the body anterior to the pectines and between the cox of the fourth pair of legs, at the same point where the penis is placed in the male (fig. 84, c.) Copulation, oviposition, and development of the ova. and reproduction of the` extremities.—Natural Observers have hitherto given but very few details respecting the man ner in which the male spider approaches the female, in accomplishing the sexual act : and wehave already observed that they have been de ceived in considering a preliminary step as the entire process. The preliminaries are accom panied with very curious circumstances, the account of which may be found in alt the me moirs and works which treat of the animals of • .
this class. It will be there seen with what precaution and fear the male makes his ap proaches to the female, who is always ready to attack and devour him, whether before or after copulation. The majority of the arachnidans deposit their eggs in great numbers. The female guards them with the utmost care, some times carries them about with her, and always prepares a silken nest for them which is fre quently covered with a solid exterior. Some arachnidans, as the scorpions for example, are ovo-viviparous; the ova are developed in the interior of the body of the female who brings forth her young possessing the faculty of loco motion ; but they rest for a certain time at tached to the hack of the mother, who guards and feeds them. and gives them a kind of edu a more or less solid texture, and it is at this part that the oviducts terminate. In the tege naria domestica, these oviducts (b, b) are con tinued internally in an insensible manner with the ovaries, which consist of a kind of bags (c, c) situated on each side of the intestinal canal, and to whose parietes the ova are attach ed in a racemose mariner. In the epeira diadema the ovaries are divided by two longitudinal membranous septa, and each is again subdivided by a transverse septum. The longitudinal sep tum has no orifice, but the transverse one is perforated. There is, therefore, no communi cation between the principal chambers of each of these ovaries, but there is a passage from the anterior to the posterior division, and the ova which are in the former must pass into the lat ter before being extruded. This structure ex
plains how it happens that the epeira diadema lays its eggs at two distinct periods. Another spider (theridion quadripunctatum, Walck.) presents a very analogous organization.
The female generative apparatus of scorpions has not hitherto been studied with that degree of care which it deserves; and there is a consi cation.
The changes which occur in the ova of spiders (aranew) have been studied with much care. We are indebted to M. Heroldt for highly interesting observations on this subject, published in the work entitled " Exercita tiones de animalium vertebris carentium in ovo formatione," folio, Marburg, 1824, from which an extract is given in the Annales des Sciences Naturelles, first series, vol..xiii. p. 250. From the importance of these re searches we here present an analysis of them.
The exterior covering of the ovum is formed by a very delicate and transparent membrane, in the composition of which no pore or fibre can be distinguished on microscopical in spection.
Within this membrane there is a liquid matter in which Heroldt has distinguished several essential parts, which in relation to their functions appear to us to correspond to the vitellus, the albumen, and the cicatricula of the egg in birds. An idea of the disposi tion and size of these parts may be formed by insnecting the subjoined figure (fig. 104), representing a vertical section of a fecundated ovum at the moment ofexclusion,and before any organ has been de veloped. The vitellus or yolk (a) forms the greatest part of the contained liquid mat ter, and the egg is almost entirely filled by it : its colour is gene rally that of yellow ochre, and sometimes has a saffron tinge. In some species the yolk is grey, white, or reddish brown ; and in each case the colour of this part determines the ge neral tint of the egg. If the yolk be consi derably magnified, it is seen to be composed of an infinite number of minute globules of various sizes, swimming in the albumen, or surrounded by it, and resembling so many small yolks.
The albumen (b) is a transparent crystalline liquid, without distinct organical parts, and consequently not presenting any globules, sur rounding the vitellus as far as the cicatricula, and intermediate in bulk or quantity to these. If an ovum be opened, and the liquid which it contains be poured out upon glass, the albu men is seen to surround the globules of the vitellus and cieatricula exactly as the serum of the blood envelopes the crassamentum. In the interior of the egg the albumen is situated, like the cicatricula, externally to the yolk, and fills the interspace between the yolk and the exterior membrane of the egg. It is in this interspace that the first lineaments of the embryo appear, and here the head, thorax, members, integuments, and their appendages; and all the internal organs, without excepting the intestines, are successively developed.