ANATOMY AND PHYSIOLOGY 33 



objects at close range or simply to distinguish between light 

 and darkness. 



Sexual Differences in Eyes. In most Diptera (Fig. 39) 

 and in Hymenoptera (Fig. 40) and Ephemeridae as well, the 

 eyes of the male are larger and closer together (holoptic) than 



FIG. 40. 



Ocelli and compound eyes of the honey bee, Apis mellifera. A, queen; B, drone. 



After CHESHIRE. 



those of the female (dichoptic). This difference is attributed 

 to the fact that the male is more active than the female, espe- 

 cially in the matter of seeking out the opposite sex. 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 tis- 

 sues of plants (many Buprestidae, Cerambycidae and Curculi- 

 onidae). Subterranean or cavernicolous insects are either eye- 

 less or else their eyes are more or less degenerate, according 

 to the amount of light to which they have access. The state- 

 ment 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 



4 



