ANATOMY AND PHYSIOLOGY 83 



entice the males by means of a characteristic odor, emanating 

 from the extremity of the abdomen. In lycsenid caterpillars, 

 an eversible sac on the dorsum of the seventh abdominal seg- 

 ment secretes a sweet fluid, for the sake of which these larvae 

 are sought out by ants. 



Wax Glands. Wax is secreted by insects of several orders, 

 but especially Hymenoptera and Hemiptera. In the worker 



FIG. 102. 



Ventral aspect of worker honey bee, showing the four pairs of wax scales. After 



CHESHIRE. 



'. .i- 



honey bee the wax exudes from unicellular hypodermal glands 

 and appears on the under side of the abdomen as four pairs 

 of wax scales (Fig. 102). Plant lice of the genus Schizo- 

 neura owe their woolly appearance to dense white filaments of 

 wax, which arise from glandular hypodermal cells. In scale 

 insects, waxen threads, emerging from cuticular pores, become 

 matted together to form a continuous shield over and often 

 under the insect itself, the cast skins often being incorporated 

 into this waxen scale. The wax glands in Coccidse are simply 

 enlarged hypodermis cells. 



Silk Glands. Larvae of very diverse orders spin silk, for 

 the purpose of making cocoons, webs, cases, and supports of 

 one kind or another. Silk glands, though most characteristic 

 of Lepidoptera and Trichoptera, occur also in the cocoon- 

 spinning larvae of not a few Hymenoptera (saw flies, ichneu- 

 mons, wasps, bees, etc.), in Diptera (Cecidomyiidse), Neurop- 



