SENSE ORGANS OF AMItTRUS. 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 25// 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 I 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 role to play. What that is remains still obscure. 

 They are chiefly developed in those forms where the skin is naked, 

 or the scales rudimentary (Lota), 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 intei-epithelial 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. 



(g) 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- 



