102 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. IT 8. — Wax-plates of Lhe honeybee 

 (After Cheshire). 



Glands opening on the surface of the body. — There are several 

 kinds of hypodermal glands, differing widely in function, that open 

 on the surface of the body; among the best known of these are the 

 following : 



Wax-glands. — The worker honeybee has fotn* pairs of wax-glands; 

 these are situated on the ventral wall of the second, third, fourth, and 

 fifth abdominal segments, and on that part of the segment which is 

 overlapped by the preceding segment; each gland is simply a disc- 

 like area of the hypodermis 

 (Fig. 1 1 8). The cuticle 

 covering each gland is 

 smooth and delicate, and is 

 known as a wax plate. 

 The wax exudes through 

 these plates and accumu- 

 lates, forming little scales, 

 which are used in making 

 the honey-comb. 



Wax -glands exist in 

 many of the Homoptera. In some of these the unicellular wax- 

 glands are distributed nearly all over the body; and the product 

 of these glands forms, in some, a powdery covering; in others, 

 a clothing of threads; and in still others a series of plates (Fig. 119). 

 Certain coccids excrete wax in con- 

 siderable quantities. China wax, which 

 was formerly an article of commerce, 

 is the excretion of a coccid known as 

 Pe-la (Ericerus Pe-la). 



Froth-glands of spittle-insects. — In 

 the spittle-insects (Cercopidcc) there 

 are large hypodermal glands in the 

 pleural regions of the seventh and eighth 

 abdominal segments, which open 

 through numerous minute pores in the 

 cuticula. These glands secrete a muci- 

 laginous substance, which is mixed with 

 a fluid excreted from the anus, and thus 

 fits it for the retention of bubbles of air 

 included in it by means of abdominal appendages (Guilbeau '08). 



Stink-glands. — Glands that secrete a liquid having a fetid odor and 

 that are doubtless defensive exist in many insects. In the stink-bugs 



Fig. 119. — Orthcsia, greatly en- 

 larged. 



