WAX GLANDS OF THE COCKROACH 573 



hypodermis, so that they stand out rather conspicuously. Fi- 

 nally, the cytoplasm becomes granular, the dense chromatin gran- 

 ules in the nucleus seem to assemble in large clumps, and the 

 nucleolus, which up to this time could not be distinguished, be- 

 comes clearly visible. The transition from normal hypodermis 

 to glandular cells can thus be readily observed in two-day-old 

 nymphs. In the third instar the condition characteristic of the 

 adult is attained, the cells being fully developed, and in some 

 cases so closely packed together as to simulate the appearance 

 of two or more layers. 



FUNCTION OF THE WAX 



The secretion of wax in insects serves various purposes — pro- 

 tection against enemies, cold, and moisture, a protection for 

 eggs, an encasement for excreta, a lining for the larval burrow, 

 etc. In the cockroach it probably serves as a protection against 

 moisture, for they live in protected places where other enemies 

 are unable to attack them. On the other hand, their presence in 

 warm, damp places intimately associated with water would seem 

 to indicate that the wax was secreted to protect them from this. 



The fact that the wax possesses the characteristic 'roachy' 

 odor suggested the idea that it might be a protection against 

 enemies on account of its smell. However, an examination of 

 beeswax and Pseudococcus wax showed that these also possessed 

 characteristic odors. That of beeswax is well known. The 

 odor. from Pseudococcus was like mouldy wet leaves. That of 

 the cockroach has already been described. From this it would 

 seem that the wax secreted by each different family of insects had 

 an odor 'sui generis.' The fact that the 'roachy' odor remains 

 in roach-infested places for a considerable period of time after 

 the roaches have been driven away or exterminated and that it 

 is difficult to remove it from dishes and kitchen utensils may be 

 accounted for by the fact that the wax remained adhering to 

 these things over which they were accustomed to run. 



The writer wishes to acknowledge his sincere thanks to Dr. 

 W. A. Riley, whose advice and criticism have been invaluable 

 and whose encouragement has made this work possible. 



