202 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES 



A study of the accompanying illustration indicates that the bee, 

 like other insects, has three body divisions — head, thorax, and abdo- 

 men, but instead of the usual three thoracic parts, there are four, 

 since one segment from the abdomen becomes fused with the thorax, 



ocellus or- 



Simple^ eye 

 Compound eye. 



ctntcnna. 



•momcCible 



Tnaxilla 

 ccndi othei^ 

 mouth ports-- 



Sting 



Worker bee, lateral view, hairs removed, showing parts of body and appendages 



on left side. (After Snodgrass.) 



leaving only six visible segments in the abdomen. The head bears 

 a pair of jointed antennae, or "feelers," large compound eyes, and 

 mouth parts much modified from the plan shown by the locust. 

 Three pairs of jointed legs and two pairs of membranous wings are 

 attached to the thorax, the wings growing out of the meso- and meta- 

 thorax. At the posterior end of the abdomen an ovipositor in the 

 female is modified in the worker into a sting, which is withdrawn 

 inside its sheath within the body when not in use. The body is 

 covered with a horny three-layered coat made up of an outer chitiii- 

 ous cuticula that covers the entire body except at the joints, where 

 it becomes membranous, thus allowing movement ; a middle layer 

 of cells called the hypodermis ; and an inner delicate basement mem- 

 brane. 



Protruding from the chitinous covering are many hairs and bristles, 

 outgrowths formed by the hypodermis, in which there are several 

 kinds of cells, some forming the chitinous coat, others the hairs, and 

 still others gland or sensory cells. In some cases the hairs are hollow 

 and contain sensory nerve endings. We must picture these animals 

 covered with heavy armor, through which sensation is impossible 



