ANATOMY AND PHYSIOLOGY 33 



Among ants of the same species the different forms may differ greatly 

 in the number of lateral facets. Thus in Formica pratensis, according to 

 Forel, the worker has about 600 facets in each eye, the queen 800-900 

 and the male 1,200. 



Blind Insects. Many larvae, surrounded by an abundance of food 

 and living often in darkness, need no eyes and have none; this is true of 

 the dipterous " maggots" and many other sedentary larvae, particularly 

 such as are internal parasites (Tachinidae, Ichneumonidae) , or such as 

 feed within the tissues of plants (many Buprestidae, Cerambycidae and 

 Curculionidae) . Subterranean or cavernicolous insects are either 

 eyeless or else their eyes are more or less degenerate, according to the 

 amount of light to which they have 

 access. The statement is made that 

 blind insects never have functional 

 wings. 



Antennae. The antennae, never 

 more than a single pair (though 

 embryonic "second antennae " occur 

 in Thysanura and Collembola), are 

 situated near the compound eyes and 

 frequently between them. With rare 

 exceptions the antennae have always 

 several and usually many segments. 

 In form these organs are exceedingly 

 varied, though many of them may 

 be referred to the types represented FlG - 43- Antennae of a moth, 



cecropia. A, male; B, female. 



in Figs. 42-44. 



Though homologous in all insects, the antennae are by no means equiv- 

 alent in function. They are commonly tactile (grasshoppers, etc.) or 

 olfactory (beetles, moths) and occasionally auditory (mosquito), as 

 described beyond, but may be adapted for other than sensory functions. 

 Thus the antennae of the aquatic beetle Hydrophilus are used in connec- 

 tion with respiration and those of the male Meloe to hold the female. 



Sexual Differences in Antennae. In moths of the family Saturniidae 

 (S. cecropia, C. promethea, etc.) the pectinate antennae of the male are 

 larger and more feathered than those of the female, and differ also in 

 having more segments (Fig. 43). Here the antennae are chiefly olfac- 

 tory, and the reason for their greater development in the male appears 

 from the fact that the male seeks out the female by means of the sense 

 of smell and depends upon his antennae to perceive the odor emanating 

 from the opposite sex. 



