ANATOMY AND PHYSIOLOGY 



75 



ecdysis is poured over the hypodermis by certain large special 

 cells, which, according to Tower, " are not true glands, but 

 the setigerous cells which, in early life, are chiefly concerned 

 with the formation of the hairs upon the body; but upon the 



FIG. 



Modifications of the hairs of bees. A, B, Megachile; C, E, F, Colletes; 

 D, Chelostoma. After SAUNDERS. 



loss of these, the cell takes on the function of secreting the 

 exuvial ,fluid, which is most copious at pupation. These cells 

 degenerate in the pupa, and take no part in the formation of 

 the imaginal ornamentation." 



Histology. The chitinous cuticula owes its existence to 

 the activity of the underlying layer of hypodermis cells (Fig. 

 88). These cells, distinct in embryonic and often in early lar- 

 val life, subsequently become confluent by the disappearance of 

 the intervening cell walls, though each cell is still indicated by 

 its nucleus. The cells are limited outwardly by the cuticula 

 and inwardly by a delicate, hyaline basement membrane; they 

 contain pigment granules, fat-drops, etc. 



Externally the cuticula may be smooth, wrinkled, striate, 

 granulate, tuberculate, or sculptured in numberless other 

 ways; it may be shaped into all manner of structures, some 

 of which are clearly adaptive, while others are unintelligible. 



