416 



HISTOLOGY 



jections which secrete a viscid fluid that causes them to adhere to what- 

 ever they touch (Fig. 377). 

 These hairs are less abun- 

 dantly developed in many 

 other insects, sometimes to be 

 used only during copulation 

 - ad. c. or for other special pur- 

 poses. In many larvae the 

 gland hairs are supple- 

 mented by various spikes 

 and hooks, all formed from 

 hypodermis cells and cuti- 

 cle, as all other external 

 arthropod tissues and organs 

 are. 



One of the most highly 

 specialized types of the 

 organs of adhesion and 



FIG. 377. Adhesive structure on foot of a beetle, 

 Hylobius. Transverse section of foot, ad.c., adhesive 

 cells whose processes (ad.p.) extend downward. (After 



SlMMERMACHER.) 



spinning may be seen in the insects as a spinning gland of various 

 larvae and adult 

 forms. These or- 

 gans are invaginated 

 portions of the 

 mouth lining, and 

 are well represented 

 by the spinning 

 gland of the larva 

 of a moth, Imperialis. 

 This gland has as- 

 sumed the form of a 

 narrow tube of some 

 length and a portion 

 of the wall of this 

 tube is shown in Fig- 

 ure 378. 



The cells are large 

 and cuboidal. They 

 form a single layer 

 lying on a fairly thick 

 basement membrane. 



The cells are so 

 large that they are 

 supplied internally with tracheal branches. One of these appears in 



FIG. 378. Portion of a longitudinal, vertical section through the 

 epithelium of a silk gland in the larva of the moth, Imperialis. 

 Three large, irregular nuclei (n.), representing two cells, are 

 shown, tr.ca., tracheal capillary with a single nucleus, tr. n., in 

 its wall (modified hypodermal nucleus) ; d., distal edge of epi- 

 thelium; b.m., basement membrane; sec.gr., secretion granules. 



