290 OTT. [Vol. VII. 



missure taken near the median line of the body the network 

 would be much more pronounced at the centre of the section 

 than toward the periphery. This is the exact appearance 

 obtained in both cross and longitudinal sections. From the 

 fact that we do not find in sections any prominent swellings 

 where the meshes of the apparent network join, from the facts 

 stated above, and also from a physiological standpoint, in that 

 impulses would be likely to be best transmitted by entirely 

 independent fibres, it seems more likely that the appearance of 

 a network in sections is obtained from a feltwork of indepen- 

 dent fibres rather than from a genuine network. 



If the interpretation that the fibres are the real nerve sub- 

 stance be accepted, the granular material surrounding the nerve 

 fibres may be regarded either as a nutrient material or as an 

 inter-fibrillar supporting material. The fact that it does not 

 appear in sections prepared by Kolliker's method to be indenti- 

 cal with the pervisceral fluid indicates that it is in part at least 

 a supporting material. 



Sense Organs. 



Stenostoma leucops has two pairs of sense organs, — the 

 ciliated pits and the dish-shaped organs. 



Ciliated Pits. — The ciliated pits are depressions of the integ- 

 ument located one on either side of the body at a distance from 

 the anterior end of the body equal to one-half its greatest width. 

 They lie opposite the anterior end of the brain (Fig. i, C.P.). 

 They open in a direction midway between dorsal and lateral, 

 and are also slightly turned forward. In the quiescent worm 

 they are shallow circular pits which, from a dorsal view, appear 

 somewhat crescentic. The walls are very contractile, and the 

 pits change their form from a broad, shallow cup to a narrow, 

 deep pit which is directed backward and inward. The change 

 of form of these pits is due both to the contraction of their own 

 walls and to the contraction of the adjacent body wall. 



In sections from a worm which was fixed in chrom-osmic- 

 acetic acid, and which were stained in haematoxylin, the pits are 

 seen to be embedded in the anterior end of the lobes of the 

 brain (Figs. 20 and 22, G.). 



The wall of each pit is made up of a single row of epithelial 



