290 



COMPAKATIVE ZOOLOGY. 



their soft, unjointed abdomen, separated from the thorax 

 by a narrow constriction, and provided at the posterior 

 end with two or three pairs of appendages, called " spin- 



Fio. 260.— A, female Spider ; B, male of same species ; C, arrangement of the eyes. 



nerets," which are homologous with legs. The oflBce of 

 the spinnerets is to reel out the silk from the silk-glands, 

 the tip being perforated by a myriad of little tubes, 

 through which the silk escapes in excessively fine threads. 

 An ordinary thread, just visible to the naked eye, is the 

 union of a thousand or more of these delicate streams of 

 silk."" These primary threads are drawn out and united 

 by the hind legs. 



The mandibles are vertical, and end in a powerful hook, 

 in the end of which opens a duct from a poison-gland in 

 the head. The maxillae, or "palpi," which in Scorpions 

 are changed to formidable claws, in Spiders resemble the 

 thoracic feet, and are often mistaken for a fifth pair. The 

 brain is of larger size, and the whole nervous system more 



