102 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. 1 1 8. Wax-plates of the 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 four 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 po,wdery 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 (Cercopidae) 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 b}^ 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. Orthesia, greatly en- 

 larged. 



