BY J. T. WILSON AND C. J. MARTIN. 673 



and whose nuclei and protoplasm stain well with haematoxylin and 

 carmine, surrounds a cuticular layer with flattened nuclei, as 

 described by Poulton. The whole is surrounded by a fibrous- 

 tissue sheath (fig. 4). The duct is frequently accompanied by 

 a leash of medullated nerves whose destination is the base of the 

 epidermic downgrowth, which the duct enters. 



The appearance and minute structure of the epidermal down- 

 growth with the duct traversing it are shown in fig. 2, which 

 represents a vertical section of the organ. As to the general 

 structure and probable significance of this downgrowth, we are in 

 entire agreement with Poulton, who considers that it represents 

 a modified hair follicle, through which the duct of the gland 

 courses to the surface. The further structural particulars which 

 we have been able to make out, tend only to strengthen Poulton's 

 ingenious hypothesis. 



The upper part of this epidermic cylinder is mostly composed 

 of plate-like epithelial cells placed vertically to the surface. 

 Poulton describes them as fusiform, but as they appear fusiform 

 both in longitudinal and transverse sections of the organ, (vide 

 our figs. 2, 5 and 6, or Poulton's figs. 8, 9, 10 in Quart. Journ. 

 Micros. Science) they must in reality be flattened plates. These 

 layers of flattened imbricated cells are arranged around the duct 

 as a centre, but -are separated from its lumen by a nucleated 

 cuticular layer, the cells of which are irregular but generally 

 flattened in the same direction as the plates (figs. 2, 5, 6, c). The 

 individual outlines of the cells of this layer are diflicult to make 

 out, and indeed in some cases (fig. 2, c) the cells appear fused. 



Outside the preceding layers of cells which form the core of the 

 epithelial cylinder, but not separated from them by any sharp 

 line of demarcation, are the investing layers of cells formed by a 

 downgrowth from the general epidermis, the layers of which turn 

 sharply downwards to form the peripheral part of the cylinder. 

 These investing la3^ers in the upper part of the cylinder consist 

 merely of epithelial plates continuous with the more superficial parts 

 of the general epidermis, (fig. 2, b) while below this there is super- 

 added a peripheral layer of more or less cubical cells formed by 



