140 



ARACHNIDANS. 



she carries them on her back during the first few days of their 

 existence, and carefully watches over their safety for upwards of 

 a month, when they become able to provide for their own sub- 

 sistence. 



The third division of the Arachnidans comprehends the well- 

 known race of Spiders, equally remarkable for their voracity and 

 their cunning. They are distinguished by having their abdomen 

 short and globular, and by its being furnished near its posterior 

 termination with a wonderful apparatus, by means of which these 

 animals manufacture silken filaments applicable to a great variety 

 of purposes and especially employed in constructing what is 

 usually named the spider's web. 



FIG. 146. NERVOUS SYSTEM OF SPIDER. 



FIG. 147. FANG OF SPIDER. 



Spiders are the implacable foes of insects, \vith which they 

 wage cruel and unremitting warfare. That the destroyer should 

 be more powerful than its victim is essential to its position ; that 

 it should excel its prey in sagacity, is likewise necessary to its 

 existence ; and by following out the same principle which has 

 been already insisted on concerning the inseparable connection 

 which exists between the perfection of an animal and the cen- 

 tralization of its nervous system, we find in the class before us an 

 additional confirmation of this law. The whole series of ganglia 

 become here aggregated together, forming, as it were, one great 

 central brain, from whence nerves radiate to all parts of the 

 body (Fig. 146). 



The mouth of the spider is a tremendous piece of machinery. 

 The mandibles (Fig. 147) are each terminated by a moveable fang, 

 which ends in a sharp point, and is perforated near its extremity 

 by a minute orifice, from which, when the spider bites, a venomous 

 fluid of great potency is instilled into the wound inflicted. Such, 

 indeed, is the malignity of this poisonous secretion, that its effects 

 in destroying the life of a wounded insect are almost instantaneous, 



