ARACHNIDA : SPIDERS. 341 



divided into rings or segments. The name Araneina 

 is from the Latin aranea, a spider. 



FIG. 465. 



Foot of Spider, magnified. 



Spiders have mandibles which end in a strong hook, in 

 the end of which there is an opening to a duct which con- 

 nects with a poison gland situated in the head. The max- 

 illae are modified for palpi, and resemble a pair of shorter 

 legs, making the spiders look as if they had ten legs instead 

 of their actual number eight. In the females the palpi 

 are simple, but in the males the terminal joint is modified 

 so as to be a sexual organ. 



Their alimentary canal is remarkable for having in 

 many cases, lateral caeca. 



Their circulatory system is quite highly organized. 

 The dorsal vessel is mainly situated in the abdominal 

 region. There is also a ventral vessel with veins or 

 sinuses which act as veins. 



The respiratory system of Spiders consists in most 

 species of both tracheae and air sacs or lung-like organs. 

 The latter are small sacs opening by transverse fissures 

 on the under side of the abdomen, near its base, and the 

 inner surface is in the form of lamellse or plates, each 



