894 ANATOMY AND DEVELOPMENT 



developed reticulum, giving with low powers a very granular 

 appearance to the nuclei. The protoplasm of the cells is also 

 somewhat granular, and the granules are frequently so disposed 

 as to produce a very well-marked appearance of striation on 

 the inner end of the cells. The pigment which gives the charac- 

 teristic colour to the skin is deposited in the protoplasm of the 

 outer ends of the cells in the form of small granules. An at- 

 tempt is made to shew this in fig. 32. 



At the apex of most, if not all, the primary wart-like papillae 

 there are present oval aggregations, or masses of epidermis 

 cells, each such mass being enclosed in a thickish capsule (fig. 

 31). The cells of these masses appear to form the wall of a 

 cavity which leads into the hollow interior of a long spine. 

 These spines when carefully examined with high objectives 

 present a rather peculiar structure. The base of the spine is 

 enveloped by the normal cuticle, but the spine itself, which 

 terminates in a very fine point, appears, as shewn in fig. 31, to 

 be continuous with the inner layer of the cuticle. In the 

 perioral region the outer layer of the cuticle, as well as the 

 inner, appear to be continued to the end of the spines. Within 

 the base of the spine there is visible a finely striated substance 

 which may often be traced into the cavity enclosed by the cells, 

 and appears to be continuous with the cells. Attached to the 

 inner ends of most of the capsules of these organs a delicate 

 fibrillated cord may be observed, and although I have not in any 

 instance succeeded in tracing this cord into one of the nerve- 

 stems, yet in the antennas, where the nerve-stems are of an 

 enormous size, I have satisfied myself that the minute nerves 

 leaving the main nerve-stems and passing out towards the skin 

 are histologically not to be distinguished from these fibrillated 

 cords. I have therefore but little hesitation in regarding these 

 cords as nerves. 



In certain regions of the body the oval aggregations of cells 

 are extremely numerous ; more especially is this the case in the 

 antennas, lips, and oral papillae. On the ventral surface of the 

 peripheral rings of the thicker sections of the feet they are 

 also very thick set (fig. 20 P). They here form a kind of pad, 

 and have a more elongated form than in other regions. In the 

 antennae they are thickly set side by side on the rings of skin 



