OF PERIPATUS CAPENSIS. 893 



THE SKIN. 



The skin is formed of three layers. 



1. The cuticle. 



2. The epidermis or hypodermis. 



3. The dermis. 



The cuticle is a layer of about O'CO2 mm. in thickness. Its 

 surface is not, however, smooth, but is everywhere, with the 

 exception of the perioral region, raised into minute secondary 

 papillae, the base of which varies somewhat in diameter, but is 

 usually not far from O'O2 mm. On the ventral surface of the 

 body these papillae are for the most part somewhat blunt, but 

 on the dorsal surface they are more or less sharply pointed. In 

 most instances they bear at their free extremity a somewhat 

 prominent spine. The whole surface of each of the secondary 

 papillae just described is in its turn covered by numerous 

 minute spinous tubercles. In the perioral region, where the 

 cuticle is smooth, it is obviously formed of two layers which 

 easily separate from each other, and there is I believe a similar 

 division elsewhere, though it is not so easy to see. It is to be 

 presumed that the cuticle is regularly shed. 



The epidermis, placed immediately within the cuticle, is 

 composed of a single row of cells, which vary, however, a good 

 deal in size in different regions of the body. The cells excrete 

 the cuticle, and, as shewn in fig. 32, they stand in a very re- 

 markable relation to the secondary papillae of the cuticle just 

 described. Each epidermis cell is in fact placed within one of 

 these secondary papillae, so that the cuticle of each secondary 

 papilla is the product of a single epidermis cell. This relation 

 is easily seen in section, while it may also be beautifully shewn 

 by taking a part of the skin which is not too much pigmented, 

 and, after staining it, examining from the surface. 



In fig. 32 a region of the epidermis is figured, in which the 

 cells are exceptionally columnar. The cuticle has, moreover, 

 in the process of cutting the section, been somewhat raised and 

 carried away from the subjacent cells. The cells of the epi- 

 dermis are provided with large oval nuclei, which contain a well- 



