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. So; 
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. 
