462 



ZOOLOGY. 



558, The arachnida have varied instincts no less remark- 

 able than those of insects ; and one feels inclined 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. 120) ; the webs which the garden spiders 

 stretch with an admirable regularity are equally curious. 

 The silk with which these animals 

 thus construct their retreats, stretch 

 snares for their prey, and form cocoons 

 for their eggs, is secreted by an ap- 

 paratus lodged in the posterior part 

 of the abdomen. This apparatus 

 consists in several packets of vessels, 

 turned on themselves, and terminat- 

 ing in pieces pierced at the summit 

 of four or six conical or cylindrical 

 mamelons called winders, and situated 

 under the anus (Fig. 500). The gluey 

 matter expelled through these pores 

 acquires consistence by the contact 

 of the air, and forms threads of ex- 

 treme 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 eselosed 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, interlaced with 

 remarkable art ; and it has been calculated that ten thousand 

 threads, as they come from the pores of one of the winders of 

 some of our common spiders, do not equal in thickness one 

 of our hairs ; whilst other species, peculiar to hot countries, 

 form nets so strong that they suffice to arrest the progress 



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

 artery ; v, venous canals. 



