LEWIS. — POLYCH^TE ANNELIDS. 253 



fibres. The results of the injection of methylen blue were studied both 

 in the living tissue and in sections prepared after treatment by the 

 ammonium-molybdate method of Bethe. 



To study the living tissue of worms that had been injected with 

 methylen blue, portions of the body wall in the head region were cut out, 

 placed upon a slide, and observed under a cover glass after adding a few 

 drops of sea water. The positions of the sense organs could be readily 

 determined, but the thickness of the cuticula prevented any satisfactory 

 conclusions as to the shape and number of the cells stained. Owing to 

 the opacity of such preparations, the central processes of the cells could 

 usually be followed only a very short distance. The sensory hairs often 

 took the blue stain. 



Two such hairs from an organ which had taken the blue stain were 

 seen in one instance to move for a considerable time, and their position 

 with reference to each other was seen to change. This was so strange a 

 phenomenon, that I asked a friend to examine the living preparation at 

 the time, and he confirmed my conclusion. So far as I know, however, 

 there exists no observation to show that sensory hairs are ever capable 

 of independent motion. 



The results obtained from sections of the methylen blue material were 

 far more complete and instructive. A comparative study of many sec- 

 tions was necessary, however, to give a satisfactory idea of a sense 

 organ. 



Often but one of the cells of the group making up an organ took the 

 methylen blue stain, and from such preparations the hasty conclusion 

 might have been drawn that only single isolated sense cells were under 

 examination. A careful examination of the cuticula, however, almost 

 always showed the presence of a concave inner edge and the doubly 

 curved outer edge characteristic of the cuticula of a sense organ com- 

 posed of several cells. In the very few cases in which this condition of 

 the cuticula did not appear, there seemed reason to believe its absence 

 due to a slight obliquity of the section. 



Sometimes the blue of the stain was concentrated upon the concave 

 inner surface of the cuticula covering the sense organ. In this way the 

 presence of several separate organs could be recognized, all other portions 

 of the cuticula remaining uncolored. 



In other instances, all or nearly all the cells of an organ would be 

 stained ; in such cases little could be made out from the thick section, 

 owin;^ to the closeness of the opaque cells. 



The most satisfactory conditions were perhaps those (Plate 6, Figs. 37; 



