Exclusion or hatching of the spider.—At length the spider bursts the egg by tearing through the exterior membrane. De-Geer' has described this phenomenon. The outer mem brane or pellicle of the ovum becomes fissured along the corslet, and the spider protrudes by this aperture, first the head, the mandibles, the thorax, and abdomen, after which there remains the more difficult operation of extracting the legs and maxillary palps from that part of the outer membrane with which these parts are, as it were, enveloped. This is at 'length effected, though slowly, by alternately dilating and con tracting the body and legs, upon which the animal is liberated, and capable of progression. In proportion as the parts are disengaged from the pellicle, it is pushed towards the extremity of the legs, and is reduced to a little white bag which is all that remains. Sometimes the pel licle is found still slightly adherent to the ab domen, but the spider soon entirely frees itself from it. This is the mode in which the young spiders of every species disembarrass themselves of the egg-covering, and the operation is analo gous to that of moulting. This is, however, only the first birth : all the parts of the spider, the head, the jaws, the legs, the abdomen, are still enveloped by a membrane which furnishes to each a sort of sheath. The spider is embar rassed in all its movements; it changes its situation with apparent pain, and is unable to construct a web and seize its prey : it seems in deed to be stupified and indisposed to action. To this end, and in order to be fit for locomo tion, it is necessary that it should free itself of this other covering; and it is only then that it can be said to see the light. This last operation, or as it may be termed the first moult, takes place after a period, varying according to the de grees of atmospheric heat and moisture. Some times it is observed within the first week, at others it is not effected before the end of several weeks. In every instance the moult takes place in the woolly nest or general envelope of all the eggs, and the young spider does not quit this common nest, except in fine weather, generally in the months of May and June.
Before arriving at the adult state the spider changes its skin many times, and even after that period it is still subject to moults, which occur every year in the spring, and after the exclusion of the eggs. Up to the present time it has been admitted that the Arachnidans, from the moment of their exclusion to their adult state, undergo no metamorphosis, but are subject only to the moultings of which we have just spoken. This circumstance has even been em ployed by zoologists as a character distinguish ing the arachnidans from the class of insects, which generally undergo metamorphoses in pas sing through the conditions of the larva and chrysalis. The observation holds good for the greater part of the Arachnidans, but there are many of this class, which, in passing to their adult condition, undergo changes which cannot but be compared with the metamorphoses of insects. Such, for example, are many of the acaridee, upon which M. Dues has recently fixed the attention of naturalists.*
We cannot conclude the present article, without briefly noticing a very curious phy siological phenomenon which has been ob served in the Arachnidans, and which has long been noticed in the class Crustacea : we allude to the faculty which these animals possess of reproducing their limbs when these have been accidentally lost. This property, which belongs to the spiders, (araneee,) was generally doubted, until a distinguished natu ralist, M. Lepelletier, published the result of his experiments ; the fact is of too much im portance in science not to be dwelt upon with some detail. Spiders which have lost a limb, according to this observer,t are always found to have lost it entirely, that is, the femur, tibia, and tarsus, are all wanting. A portion of a leg is never found detached at one of its joints,nor bro ken off between two joints, nor the femur remain ing adherent to the body by itself, or with the tibia, the rest of the leg being lost. If by accident a spider should be met with in any of these con ditions, it is either dying or dead. But M. Lepelletier remarks that those which have lost one or more entire legs, are not less lively on that account.
To explain these circumstances our author commenced a series of experiments on spiders, in the year 1792, with the following results:— The smallest wound in the thorax or abdo men of a spider is mortal, and that in a very short time, on account of the loss of the internal nutrient fluid, which cannot be staunched.
If a 'leg of a spider be cut off with a sharp instrument either at one of its joints, or in the interval of two, leaving a part of the limb ad hering to the body, the spider appears to suffer considerably ; it endeavours to tear off the rest of the leg ; if it succeeds, it again acquires its powers of moving, and the hemorrhage soon ceases ; in the contrary case it perishes in twenty-four hours.
The luxation of one of the joints, or the frac ture of the femur or tibia in the middle are equally mortal, if the spider does not soon dis embarrass itself of the leg which has received the injury.
It is necessary here to make a remark upon the anatomy of the legs of spiders and crusta ceans ; they have the first joint short, which connects the leg to the thorax ; M. Lepelletier calls this the haunch, coxa. If a spider be seized by the extremity of one of its legs, and is left at liberty to make its efforts to escape, the leg will be separated from the body at the junction of the femur with the coxa ; and the same thing takes place when the body of the spider is held fast, and the leg is pulled off. In both these cases the spider seems not to suffer pain ; it experiences only a very little loss of the internal fluid, and does not die in consequence ; it spins, seizes its prey, and oviposits in the or dinary manner.
The preceding facts are applicable to all spiders, (aranece,) and M. Lepelletier has ob served them repeatedly in many of the common species. The following experiments have been made only on the domestic spider, (Tegenaria domestics, Walck.) because it can be preserved in a lively condition, and for many years in a glass vessel.