8 



APPLIED ENTOMOLOGY 



the mouth beneath are called hypognathous : those with it in front are 

 prognathous. 



Structures found on the head are a pair of antennae, the two compound 

 eyes, ocelli, and the mouth parts. On the thorax are the wings and legs; 

 and on the abdomen are various organs such as the ovipositor, sting, cerci, 

 styli, etc., present in some cases; absent in others. 



FIG. 13a. Different forms of insect antennse. (Original.) 



Antennae are nearly always present. They are usually slender, jointed 

 and therefore more or less flexible organs, varying greatly in the number of 

 segments composing them. They are sometimes very short; sometimes 

 long; often thread-like; sometimes enlarged near the tip; in many cases 

 with fine branches either on one or both sides, so that they resemble 

 feathers or plumes; rarely they fork; in fact are of 

 many forms (Fig. 13) . Sense organs are present on 

 them for the sense of touch, and probably also for 

 smell and hearing, at least in some cases. 



The eyes are of two kinds. There is a pair of com- 

 pound eyes, each of which is a group of similar struc- 

 tures which usually are like tall, slender pyramids in 

 form. Only the bases of these pyramids show on the 

 surface, the remainder being within the head. The 

 bases, closely pressed together, are usually more or 

 less hexagonal, and their outlines can often be easily 

 seen with a magnifying glass. They are called facets, 

 and the eyes themselves are sometimes termed the 

 facetted eyes. 



The other kind of eyes, called ocelli, may be absent, 

 or if present, may vary in number in different insects, 

 three being perhaps the most usual. Each, as seen from the surface, 

 is a nearly circular, convex spot about the size of one of the facets of a 

 compound eye. It may be larger than this, but is never equal to an 

 entire compound eye in size. In some cases a cluster of ocelli or of the 

 pyramids of the compound eyes is found, not closely pressed together 



FIG. 136. An- 

 tennse of Cecropia 

 Moth. (Samia ce- 

 cropia L.) About 

 twice natural size. 

 (Original.) 



