WAX GLANDS OF THE COCKROACH 569 



At the anterior end of each segment — that part which is over- 

 lapped by the preceding segment — the modified hypodermal cells 

 are especially well developed, often producing the appearance 

 of two or more layers of cells, no doubt due to the crowding of 

 the individual cells, with the consequent displacement of their 

 nuclei (figs. 8 and 9). This is best seen on the ventral side of 

 the male where the cells are closely packed together so that there 

 seems to be no order to their arrangement. In such places the 

 cells also appear of different sizes, no doubt due to the fact that 

 a single section did not pass through the middle of each cell. In 

 other places they are but a single layer in thickness. 



These modified hypodermal cells possess large vesicular nuclei 

 with relatively thick nuclear walls, and provided with a nucleolus 

 and many deeply stained chromatin granules (fig. 10). Their 

 cytoplasm is also coarsely granular in appearance, and contains 

 several vacuoles. As a rule, they are cuboidal or colmnnar, 

 except where crowding together has caused them to assume vari- 

 ous forms. Scattered here and there between these cells and 

 the overlying cuticula, or intercalated somewhat between them 

 at their upper surface, are the non-glandular hypodermal cells 

 with nuclei similar to those in the intersegmental areas. 



Posterior to that portion of the segment which is overlapped 

 by the preceding segment, the normal hypodermal cells are in 

 the majority, while here and there scattered among them are 

 large modified cells similar to those occurring at the anterior end 

 of the segment. Where such cells occur, the ordinary hypoder- 

 mal cells are absent or else are somewhat crowded together. 



From the foregoing observations, therefore, it will be seen 

 that the body wall of the cockroach does not differ materially 

 from that of other insects, being composed of a cuticula, a hypo- 

 dermis consisting of a single layer of ceUs, and a basement mem- 

 brane. However, many of the hypodermal cells have become 

 specialized, increasing in size, so that in places, particularly on 

 the ventral side of the male, they present the appearance of two 

 or more layers. The cytoplasm of these cells has become strongly 

 granular while the nuclei have become large and vesicular. Their 

 entire structure, therefore, indicates that they are secretory in 



THE joi:rnal of morphology, vol. 31, NO. 3 



