LEWIS. — P0LYCHJ3TE ANNELIDS. 251 



unite. In certain regions of the worm these cells are greatly elongated 

 and very slender. Those shown in Figures 63-65 were stained in 

 methylen blue. 



b. Gland Cells. 



The gland cells (Plate 3, Figs. 17-20) are especially numerous in 

 the fifth to the ninth segment of the body inclusive. They also show 

 great variation in size and shape. The gland pore, situated at the free 

 end of the cell, is readily seen in sections (Fig. 18) or in mounted 

 specimens of removed cuticula (Fig. 19). 



c. Sense Organs. 



I propose to describe the sense organs somewhat minutely. Their ap- 

 pearance will be considered, first, in the removed cuticula ; secondly, in 

 sections prepared by ordinary methods and by the vom Rath fixative ; 

 and, thirdly, in methylen blue preparations. Conclusions as to their finer 

 structure and their probable functions, and a historical review follow. 



(1) Cuticula. 



A study of the removed cuticula shows that it is everywhere made up 

 of two systems of fibres, which cross each other at an angle of about 

 90° (Plate 3, Fig. 19). Both systems are continuous, though faint, over 

 each sense organ. The position of the sense organs is marked by a differ- 

 entiation of the cuticula, which is nearly circular in outline. The cuticula 

 of these areas is much reduced in thickness, but seems to be more highly 

 refractive than the surrounding cuticula. No gland pores are present in 

 these circular areas, but study with high powers reveals a number of very 

 minute openings, — the canals through which the sense hairs pass. The 

 number of these canals varies. I have counted as many as nine or ten 

 in a single area. The diameter of the areas varies from S/x to 16u, and 

 may even exceed this size. Frequently one or more cells from a sense 

 organ are left hanging to the dried cuticula ; in such cases the slender 

 peripheral cell-process running up to the pore canal may be readily made 

 out. Figure 19 (Plate 3) is a camera drawing showing the appearance 

 of the surface of a portion of the cuticula including one of these areas, 

 made from the removed cuticula of Axiothea torquata. A section per- 

 pendicular to the surface of the body through one of the sense ororans, 

 from material fixed with the vom Rath fluid, is shown in each of the 

 Figures 17 and 18 at the top of Plate 3. From these, as well as from 

 Figures 35-46 (Plate 6) and 48-52 (Plate 7), it is to be seen that im- 



