ARACHNIDA. 



211 



the valve certain organs of a singular structure 

 which are called combs, pectines, (jig. 84, d>) 

 on account of the disposition of a series of 

 small appendages of which they are formed, 

 and which are arranged on the lower surface 

 one beside the other, like the teeth of a comb. 

 Many speculations have been offered respecting 

 their uses. Many naturalists believe that they 

 render some assistance in the act of impregna- 

 tion. Some suppose that they are extended 

 during progression, and prevent the abdomen 

 of the scorpion from trailing on the ground : 

 others, again, regard them as hygrometrical 

 organs, by means of which the animal judges of 

 the humidity of the atmosphere. These are, 

 however, all mere gratuitous hypotheses un- 

 supported by any observation ; and the fact is 

 that we have yet to learn the use of these pec- 

 tinated appendages. 



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,J which are closed by opercular pieces of 



Fig. 103. 



a more or less solid texture, and it is at this 

 part that the oviducts terminate. In the tege- 

 nar'ia domestica, these oviducts (b, bj 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 manner. 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- 



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 coxae of the fourth pair of legs, at 

 the same point where the penis is placed in the 

 male (Jig. 84, c.) 



Copulation, oviposition, and development of 

 the ova. Metamorphosis, 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 all 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 back of the mother, who guards 

 and feeds them, and gives them a kind of edu- 

 cation. 



The changes which occur in the ova of 

 spiders (araneae) have been studied with much 

 care. We are indebted to M. Ileroldt 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 inspecting the subjoined figure (Jig. 104), 



p 2 



