72 ENTOMOLOGY 



they have no influence upon flight, as Mayer has proved, and appear to 

 be useful chiefly as a basis for the development of color and color 

 patterns which are not infrequently adaptive. 



Androconia. The males of many butterflies, and the males only, 

 have peculiarly shaped scales known as androconia (Fig. 99) ; these are 

 commonly confined to the upper surfaces of the front wings, where they 

 are mingled with the ordinary scales or else are disposed in special 

 patches or under a fold of the costal margin of the wing (Thanaos). 

 The characteristic odors of male butterflies have long been attributed 

 to these androconia, and M. B. Thomas has found that the scales arise 



FIG. 100. Section across tarsus of a beetle, 

 Hylobius, to show bulbous glandular hairs. 



After SlMMERMACHER. 



hy 



FIG. 10 1. Stinging hair of a caterpillar, 

 Gastropacha. c, cuticula; g, gland cell; h, 

 hair; hy, hypodermis. After CLAUS. 



from glandular cells, which doubtless secrete a fluid that emanates 

 from the scale as an odorous vapor, the evaporation of the fluid being 

 facilitated by the spreading or branching form of the androconium. 

 Similar scales occur also on the wings of various moths and some 

 Trichoptera (Mystacides) . 



Glands. A great many glands of various form and function have 

 been found in insects. Most of these, being formed from the hypoder- 

 mis, may logically be considered here, excepting some which are inti- 

 mately concerned with digestion or reproduction. 



Glandular Hairs and Spines. The presence of adhesive hairs on 

 the empodium of the foot of a fly enables the insect to walk on a smooth 

 surface and to walk upside down; these teneni hairs emit a transparent 

 sticky fluid through minute pore canals in their apices. The tenent 

 hairs of Hylobius (Fig. 100) are each supplied with a flask- shaped unicel- 

 lular gland, the glutinous secretion of which issues from the bulbous 



