290 
COMPARATIVE 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- 
Fig. 260.—A, female Spider; B, male of same species; C, arrangement of the eyes. 
nerets,” which are homologous with legs. The office 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. 150 These primary threads are drawn out and united 
by the hind legs. 
The mandibles are vertical, and end in a powerful liook, f 
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 
