THE ANATOMY. EPIDERMIS 13 



These latter are pointed at one extremity, the fine process running up between 

 the other cells ; these cells are termed by Ceefoxtaine ' cellules de remplacement,' 

 inasmuch as they appear to replace the other cells of the outer layer. The outer 

 layer itself is composed of two sorts of cells, of large oval glandular cells and of the 

 interstitial cells ; the former are large oval cells filled with numerous granules ; the 

 basal portion of the cell, in which lies the nucleus, is more protoplasmic and is narrower 

 than the swollen upper part ; the cell ends above in a fine prolongation which opens 

 through a pore on the cuticle. The interstitial cells are of much less diameter; they 

 often appear in cross sections to have excavated surfaces ; and in fact they are moulded 

 to the form of the glandular cells which lie amongst them. The distal extremity 

 of these cells is frequently prolonged or rather frayed out into a number of fine 

 processes which seem to be in connexion with nerves. The cells of the epidermis are 

 imbedded in a homogeneous connecting substance, which is more evident where the cells 

 diverge from each other at the point of contact with the cuticle. This connecting sub- 

 stance leaves a polygonal mesh work upon the cuticle, which is visible when the latter 

 is viewed from the under surface. The cuticle seems undoubtedly to be a formation 

 of the packing cells of the epidermis ; the pores upon its surface are the outlets of 

 the gland-cells, and their existence appears to be simply due to the fact that the 

 gland-cells do not secrete a cuticle like the other cells, their secretory activity being 

 taken up in the formation of the granules with which they are laden ; hence at the 

 points where they abut upon the cuticle there are gaps — the pores in question. The 

 cuticle is sometimes distinctly to be seen as a double laj'er; viewed superficially it 

 is seen to be traversed by two sets of striae, crossing each other at a right angle ; 

 these striae correspond to two sets of fibrils, which are not upon the same plane, 

 and therefore give rise to the double layer already referred to. 



The striation is thus not merely an optical efiect, but is due to the composition of 

 the cuticle out of numerous fine strands of cuticular substance. 



Clitellar epidemiis. The epidermis on the clitellum is modified in structure. In 

 Lumbricus it has been described, especially by Clapabede, Horst, Mosjisovics, 

 Cerfontaine, and quite recently by Cole. 



The clitellum in the most fullj' developed portion, that is to say on the back 

 of the animal, is made up of several layers of glandular cells. There are first of all 

 elongated gland-cells of cylindrical form, which ai-e filled with granules, save at the 

 inner extremity which is protoplasmic, and contains the nucleus. These gland-cells 

 do not extend for a great distance into the thickness of the clitellar epidermis ; below 

 them are the second sort of cells which are massed together into columns ; there 

 are several layers of these cells, and the axes of the columns which they form are 



