564 E. H. DUSHAM 



ing. That they have been able to Uve in moist places and also 

 withstand submerging would lead one to suppose that their 

 bodies were protected by some oily or waxy secretion. 



HISTORICAL 



The study of the wax glands of the cockroach is bound up in 

 a controversy as to the number of layers m the hypodermis of 

 these insects. In insects in geniqral the body wall is relatively 

 smiple, consisting of an outer chitinous covering or cuticula, the 

 hypodermis consisting of a single layer of cells, and the basement 

 membrane, and as such, Miall and Denny described it in their 

 work on the cockroach, in which they stated that the hypodermis 

 consisted of a single layer of flattened cells, resting on a basement 

 mebrane, each cell corresponding to a polygonal area of the 

 overlying cuticula. 



In 1888, however, E. A. Minchin, while studying certain 

 glands on the dorsal side of the cockroach, found that the hypo- 

 dermis, at least on the dorsal side of the older stages of the male, 

 consisted of two layers everywhere except in the intersegmental 

 areas where only a single layer was present. In certain places 

 he found that the cells of these layers had the appearance of 

 giant cells with large nuclei, granular contents, and elongate 

 processes. These he interpreted as ganglion cells. He found 

 them scattered over each tergum, especially at the anterior por- 

 tion of each tergite — that part which is overlapped by the pre- 

 ceding tergite — although they were also scattered throughout 

 the region posterior to this part. Between these so-called gang- 

 lion cells he found the ordinary cells of the hypodermis. He 

 therefore concluded that in the cockroach, at least, the hypo- 

 dermis consisted of an upper layer of cells corresponding to the 

 polygonal areas of the cuticula, and a lower very irregular layer, 

 occasionally forming two layers, whose cells were modified to 

 form nerve cells, and which were probably connected with setae 

 where the terga were exposed. 



In 1889, Mingazzini made a detailed study of this apparently 

 double-layered hypodermis in order to verify Minchin's work, 



