252 PROCEEDINGS OF THE AMERICAN ACADEMY. 



mediately over the sense organs the cuticula is of less than half its usual 

 thickness. It is deeply concave on the inner surface, and shows on the 

 exterior a slight convexity, which is usually surrounded by a shallow cir- 

 cular depression. 



(2) Sensory Cells. 



After having given considerable attention to the matter, I have 

 come to the conclusion that the sense organs of Clymene producta and 

 Axiothea torquata are invariably composed of a number of spindle- 

 shaped cells, — that there are no single or isolated sensory cells. The 

 best general view of the sensory organ is obtained from sections per- 

 pendicular to the surface of the worm, made from material fixed in 

 vom Rath's mixture, such as is shown, in part, in Figures 17 and 18 

 (Plate 3). From sections of this kind it is to be seen that each sensory 

 organ is composed of a small number — usually a dozen or less — of 

 closely grouped spindle-shaped cells traceable through nearly the whole 

 thickness of the epidermis. Near their basal ends these cells may take 

 different directions, so that the bundle becomes dissolved before reaching 

 the basement membrane. In such sections the exact shape of that por- 

 tion of the sensory cell which lies next the cuticula could not be fully 

 made out ; but the grouping of the cells, the spindle-shaped body of each 

 cell, and the sensory hairs passing through the cuticula, are all plainly 

 visible. By no other method were the sense hairs so satisfactorily 

 shown. Occasionally (Fig. 17) the cuticula is slightly pulled away from 

 the cells of the sense organs, and in such cases the sensory hairs may 

 remain in the cuticula, projecting beyond its free surface. Although the 

 exact form of the peripheral portion of each cell could not be satisfac- 

 torily made out from such sections, yet enough could be seen to show 

 that the cells are elongated and spindle-shaped, tapering both above and 

 below the nucleus, which is oval, rather large, and contains a single 

 nucleolus. Near the cuticula, the cells are closely pressed together, their 

 peripheral ends being evidently very slender. In most cells the nucleus 

 is situated at about half the height of the epidermis, but in some it may 

 be near the cuticula and in others sunk to the base of the epidermis. 

 This difference in the position of the nucleus is often shown in the differ- 

 ent cells making up a single organ. 



(3) Besuhs ofMethjlen Blue Method. 



The application of the methylen blue method confirmed the results ob- 

 tained by other methods, and gave much additional information concern- 

 ing the individual cells of the sense origans and their relation to nerve 



