30 



THE COCKROACH : 



laminae, secreted by an underlying epithelium, or " chitino- 

 genous layer." This consists of a single layer of flattened cells, 

 resting upon a basement membrane. A cross-section of the 

 chitinous layer, or "cuticle," examined with a high power 



A 



677* 



Fig. 8. Diagram of Insect integument, in section, bm, basement membrane ; 

 hyp, hypodermis, or chitinogenous layer ; ct, ct', chitinous cuticle ; s, a seta. 



shows extremely close and fine lines perpendicular to the laminae. 

 The cells commonly form a mosaic pattern, as if altered in 

 shape by mutual pressure. The free surface of the integument 

 of the Cockroach is divided into polygonal, raised spaces. Here 

 and there an unusually long, flask-shaped, epithelial cell projects 

 through the cuticle, and forms for itself an elongate chitinous 

 sheath, commonly articulated at the base ; such hollow sheaths 

 form the hairs or setae of Insects structures quite different 

 histologically from the hairs of Vertebrates. 



The polygonal areas of the cuticle correspond each to a 

 chitinogenous cell. Larger areas, around which the surrounding 

 ones are radiately grouped, are discerned at intervals, and these 

 carry hairs, or give attachment to muscular fibres. 



Viallanes (loc. cit.) has added some interesting details to what 

 was previously known of Insect-hairs. There are, he points 

 out, two kinds of hairs, distinguished by their size and struc- 

 ture. The smaller spring from the boundary between contiguous 

 polygonal areas, and have no sensory character. The larger 

 ones occupy unusually large areas, surmount chitinogenous cells 

 of corresponding size, and receive a special nervous supply. 



