OF THE CLASS ARACHNIDA. 



419 



her back when they are too feeble to walk alone. All these 

 animals undergo several moultings before reaching the adult 

 age, and some experience a sort of metamorphosis ; for there 

 are of them whose limbs at first are only three pairs in num- 

 ber, but which acquire a fourth at a more advanced age. 



558. The arachnida have varied 

 instincts no less remarkable than 

 those of insects; and one feels in- 

 clined to accord to them still higher 

 faculties, for animals of this class 

 have been seen capable of a kind of 

 education, and to give signs of a 

 sort of intelligence. Many amongst 

 them have recourse to particular 

 tricks to secure their prey, and 

 others display in the construction of 

 their dwelling a singular industry. 

 We have already had occasion to 

 speak of the remarkable nest of the 

 mygale (Fig. 102) ; the webs which 

 the garden spiders stretch with an 

 admirable regularity are equally cu- 

 rious. The silk with which these ani- 

 mals thus construct their retreats, stretch snares for their prey, 

 and form cocoons for their eggs, is secreted by an apparatus 

 lodged in the posterior part of the abdomen. This apparatus 

 consists in several packets of vessels, turned on themselves, and 

 terminating in pieces pierced at the summit of four or six 

 conical or cylindrical mamelons called winders, and situated 

 under the anus (Fig. 414). The gluey matter expelled 

 through these pores acquires consistence by the contact of 

 the air, and forms threads of extreme tenuity, and of a very 

 great length. By the aid of its limbs the animal reunites 

 into a single cord a multitude of these threads, and each 

 time that, in balancing itself, these winders come to touch 

 the body on which it rests, they attach to it the extremity of 

 one of these threads, the opposite end of which is still 

 enclosed in the secretory apparatus, and the length of which 

 it may consequently augment at pleasure. The colour and 

 the diameter of the thread varies much : a spider of Mexico 

 constructs a web composed of red, yellow, and black threads, 



* Abdomen and Heart of a Spider : a, abdomen ; c, heart : ar, cephalic 

 artery ; v, venous canals. 



EE2 



Fig. 415.' 



