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¬ 
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 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 fora fifth pair. The 
brain is of larger size, and the whole nervous system more 
