188 AEACHNIDA. 



Spiders are the implacable foes of insects, with 

 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 per- 

 fection of an animal and the centralization of its ner- 

 vous system, we find in the class before us an addi- 

 tional 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. 



The mouth of the spider is a tremendous piece of 

 machinery. The mandibles, or jaws, are each ter- 

 minated by a moveable 

 fang, which ends in a 

 sharp point, and is per- 

 forated near its ex- 

 tremity by a minute 

 orifice, from which, 

 when the spider bites, 

 a venomous fluid of 



FlG. 147. FANG OF SPIDER. 



great potency is in- 

 stilled 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, and in the case of some large species, 

 even small birds fall victims to its virulence. 



One peculiar characteristic of spiders, as we 

 have already stated, is the possession of a spinning 

 apparatus, whereby the threads composing their web 

 are manufactured. The apparatus employed for this 

 purpose is situated upon the hinder part of the 

 abdomen, and consists externally of four spinnarets, 

 from which delicate threads, represented in the 

 accompanying figure, are produced. 



Each spinnaret when highly magnified is found to 

 be perforated at its extremity by innumerable orifices 



