220 



INSTINCTS OF ARACHNIDA. 



palpi, whose use appears to be very important ; a great number 

 of these animals envelop their eggs in a cocoon of silk ; and 

 sometimes the mother remains with her young family to protect 

 it, and even carries the young ones on her back when they are 

 too weak to walk. All these animals undergo several changes 

 before they arrive at adult age ; and certain of them experience 

 a species of metamorphosis, for there are some, whose limbs 

 consist at first of only three pair, and which acquire a fourth at 

 a period more or less advanced. 



821. The Arachnida are endowed with varied instincts, which 

 are sometimes notless remarkable than those of Insects; and weare 

 perhaps even to attribute to them higher faculties; for some animals 

 of this class are capable of undergoing a kind of education, and 

 give evidences of a certain degree of Intelligence. Several of them 

 use particular stratagems to carry off their prey ; and others 

 display singular industry in the construction of their habitations. 

 We have elsewhere had occasion to speak of the remarkable nest 

 of the Mygale ( ANIM. PHYSIOL. 700) ; and the webs which our 

 garden Spiders spread with such admirable regularity, are 

 equally curious. The silk with which these animals thus con- 

 struct retreats for themselves, spread snares for their prey, and 

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

 in the posterior part of the abdomen. This apparatus consists 



of several bundles of vessels, twisted 

 together, and terminating in minute 

 apertures, which are pierced at the 

 summit of four or six conical or 

 cylindrical projections, called spin- 

 nerets, and situated at the end of 

 the tail. The gluey matter thrown 

 out through these pores, acquires 

 consistency by its contact with the 



air, and consists of threads of an 



Fi. 548. NEST OF MYGAI>K. 



extreme fineness, and a length not 

 less remarkable ; by the help of its 

 feet, the animal collects a number of 



these threads into a single cord ; and each time that, in balancing 

 itself, the spinnerets touch the body upon which it rests, it there 



