14 Journal of Comparative Neurology. 



few cells and peripheral processes which were untouched by the 

 blue but are now stained a deep pink by the cochineal (Plate 

 II, Fig. 32). In these cases it can not only be seen that the 

 bodies of these cells, like those stained by the blue, lie entirely 

 within the epidermis ; but that, in the body epidermis, all the 

 bodies of the cells of a sense-organ generally lie above the middle 

 height of the epidermis. I have seen but very few of these sense- 

 organs whose cell-bodies reached almost to the base of the epi- 

 dermis. The cells stained by the blue sometimes lie in the 

 center, sometimes in one or both margins of an organ ; the cells 

 stained pink are not only exactly like the others but clearly 

 send peripheral processes into the cuticular cavity over each 

 sense-organ : it would therefore appear that each diffuse sense- 

 organ is composed of but one kind of cell and that cell is clearly a 

 bipolar nerve-eell. The epidermal cells around an organ show 

 no signs of being modified into covering cells. 



In forty organs especially examined for this point in sec- 

 tions of the peristome, only three showed but a single blue cell. 

 Such cases might at first sight be taken as proof of the exist- 

 ence of isolated sensory cells, but in each of these three cases 

 around the single blue cell there were found, by the use of the sec- 

 ondary stain, other cells which presented the same characteris- 

 tic appearances as the blue cell. Moreover, whenever the cuticu- 

 lar cavity belonging to the organ in question appeared in the 

 same section, there were found in this cavity not only the blue 

 stained process of the blue cell, but also other peripheral pro- 

 cesses untouched by the blue. These processes were entirely 

 free from pigment, which is always found in the peripheral ends 

 of the supporting cells of the epidermis — therefore they cannot 

 belong to the common cells of the epidermis. In hundreds of 

 diffuse sense-organs examined for various purposes, I have 

 always found more than one cell. I therefore consider that I 

 am justified in deciding that in the body epidermis of Nereis 

 virens there are 710 isolated sensory cells, the bipolar 7ierve cells 

 there present are all grouped into definite sense-orgatts. 



