ANAT< 



other terrestrial beetle^ .,)' | In illy. ;i < 



divided into minuti wlii< li t lion 



unerate type commonly more or L -^onal 



( Fi.u. -nil of mutual |>n 



|iial in 9126, f<r in dragon \Y\c^ thedol fre- 



quently larger than the ventral. In diame- 

 ter tin- fart-Is rani^c from .oif> mm. (Lycana) 

 to .o<)4 mm. (Ccraittbyx). Their number i> 

 often enormous; thus the house lly '.I/ 

 </<>;;/<\v//V/ ) ha- .j.ooo to each eye, a butterfly 

 (I\ipilio} i/vooo, a beetle (Mordclhi) 25,000 

 and a sphingidmoth 27,000; ontheother hand, 

 ants have from 400 down, the worker ant of 

 Eciton having at most a single facet on each 

 sick 1 of the head. 



Ocelli. The simple eyes, or ocelli, appear 

 as small polished lenses, either lateral or dor- 

 sal in position. Lateral ocelli (Fig. 39) occur 



y/ . FIG. 39- HeacUof, a cater- 



in the la r ViU Of most holometaboloUS insects pillar Samia cecropia, to show 



and in parasitic forms. Dorsal ocelli, sup- lateral ocelli 

 plementary to the compound eyes, occur on or near the vertex, and 

 are more commonly three in number, arranged in a triangle, as in 

 Odonata, Diptera (Fig. 40) and Hymenoptera (Fig. 41) as well as many 

 Orthoptera and Hemiptera. Few beetles have ocelli and almost no 



40. Ocelli and compound eyes of a fly, Phormia regina. A, male; B, female. 



butterflies (Lerema accius with its one ocellus being the only exception 

 known), though not a few moths have two ocelli. 



\- explained beyond, the compound eyes are adapted to perceive 



torm and movements and the ocelli to form images of objects at close 

 ran.u r e or simply to distinguish between light and darkness. 



Sexual Differences in Eyes.- In most Diptera (Fir. 40) and in 

 Hymenoptera i Fig. 41) and Fphemerida- as well, the eyes of the male arc- 



