108 INSECTS. 



Structure. Observe that the body is divided into two 

 regions. The anterior one is the cephalothorax. As the 

 name indicates, it corresponds to both head and thorax 

 of insects proper. The posterior region is the abdomen. 

 Observe the relative size and shape of the two divisions, 

 and on the lower side of the body find the pedicel con- 

 necting them. 



I. Cephalothorax. On the anterior prominence of the 

 cephalothorax find the eyes. With a lens make out their 

 number, kind, and arrangement. 



Examine the two large mandibles that hang down from 

 the front of the cephalothorax, attached above, and free 

 below. Study their action. Find a strong, incurved 

 poison fang at the lower end of each. These fangs are 

 hollow, and into the wounds they make is poured a poison 

 secreted by glands situated in the bases of the mandibles. 



Observe (from below) a pair of jointed maxillary palpi 

 arising behind the mandibles, and extending forward, 

 appearing like a pair of dwarfed legs. Observe that their 

 basal segments are movable upon each other, and closely 

 surround the mouth. These, by rubbing together, assist 

 in comminuting food, and are called maxillae. Find, in 

 all, six segments in each palpus. 



Find eight legs, and in each one seven segments. Ob- 

 serve the size and arrangement and action of the legs. 



Examine the terminal segment to discover by what means 

 the spider is able to run easily over webs which hopelessly 

 entangle other insects. Find two pectinated claws, and 

 (sometimes) a third, which fits, forceps-like, against them. 



II. Abdomen. On the under side, just behind the hind- 

 most pair of legs, and on either side of the median ventral 

 line, find two smooth, hard patches covering the openings 

 to a pair of breathing organs. Each breathing organ is a 

 sort of rudimentary lung, through the leaves of which the 

 blood flows for aeration. 



