wont ail 
ANATOMY AND PHYSIOLOGY. 65 
Commencing, therefore, with the head, which 
corresponds to the first larval segment :—The chief 
parts to be noticed here are the eyes, the mouth 
in all its details, and the antenne. The horny 
skeleton to which these are attached has different 
names in different parts: the elementary divisions of 
the head, however, have not in wasps the same 
importance as those of the thorax have, and we need 
not dwell on them at length. The face is a more 
intelligible expression as applied to wasps, which have 
the head set at right angles to the axis of the body, 
than to many other insects. Beetles, for instance, 
have the mandibles projecting forwards, and their face 
is on the same plane as their back, the vertex of their 
head being buried in the thorax. But the vertex of 
the wasp’s head, as she stands, is its highest part. 
There seems, at first, little to notice in this round 
dark downy surface; but if we look closely we shall 
tg see three little shining points, black, or occasionally 
marked with yellow, set in the form of a nearly equi- 
lateral triangle with the apex pointing forwards. 
These are called the ocelli, or simple eyes, to dis- 
tinguish them from the large compound eyes which 
stand out from either side of the head of the perfect 
insect. ‘The larva has only simple eyes; these, how- 
ever, are not the ocelli, but the rudiments of the 
compound eyes, into which they are developed, and 
like which they stand, two in number, one on either 
side of the head.* 
The eyes of insects have been most successfully © 
studied by Miiller,t whose description I propose to 
* Westwood. ‘ Entomologist’s Text-book,’ p. 184. 
t ‘ Burmeister Trans.,’ pp. 289 — 295. 
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