SENSE ORGANS OF AMIURUS. 255 
far the granular substance has lost much of its granular appearance, 
has become more homogeneous, and takes on a slight stain from vari- 
ous reagents (red from picrocarmine) which it formerly refused to do. 
The larger clavate cells may attain a length of 100%, when the 
nucleus if single may be as much as 25y in diameter, while if two 
be present they are rarely more than half that size. The nucleus 
is generally vesicular, having a distinct membrane, a single distinct 
nucleolus and a scanty nuclear network, all of which stain with the 
ordinary nuclear reagents. In spite of the very favourable size for 
such purpose, and of the fact that nuclei are present in all stages of 
division, I have not been able to make out distinct nuclear figures ; 
but when the chromatin is not disposed of as above it appears to 
be scattered in figures, in which it is impossible to detect any plan. 
Occasionally four nuclei are met with instead of two, and IT have 
even met with cells containing a greater number, without any indica- 
tion of subdivision of the cell itself. 
There can hardly be any doubt that the clavate cells have an im- 
portant physiological rdle to play. What that is remains still obscure. 
They are chiefly developed in those forms where the skin is naked, 
or the scales rudimentary (Zofa), and no doubt they are engaged in 
the secretion of some substance which acts as a protection in lieu of 
these. Their reaction to various staining fluids indicate that this 
secretion must be very different from that which is the product of 
the ordinary mucus-cells which are present everywhere throughont 
the class. Perhaps Pfitzner’s suggestion that the secretion may be 
poured out into the interepithelial spaces so as to prevent the entry 
of water may not be very far from the truth. It is certain at least 
in Amiurus that there is no aperture to the clavate cell such as the 
mucus-cell possesses, and their position indicates that lubrication of 
the surface is not their function. Occasionally a clavate cell may be 
seen in sections protruding from the surface (Fig. 2), but such 
appearances are probably due to a defect in the superficial layers of 
the epidermis, and to the action of the hardening reagents. 
(9) Interepithelial Pigment-Cells—I do not remember to have 
seen the source of these cells discussed ; it is possible that develop- 
mentally they may belong to the next group. In young stages the 
interepithelial pigment is very abundant, forming a continuous net- 
work of cells only interrupted by the cutaneous sense organs. In 
the adult skin the individual cells are more independent, and gen- 
