388 E. S. GOODRICH. 



my specimens alive. A detailed descriptiou will, therefore, be 

 first given of the organ in this species, which will then be 

 compared with some other members of the family. 



If the fresh worm be killed, laid out, and slit up on the 

 dorsal surface on each side along the bases of the parapodia, 

 and a piece of the strip so obtained be placed with the inner 

 surface upwards on a slide and examined under the microscope, 

 there will be seen running transversely on either side, and 

 curving round the outer edge of the great longitudinal muscles, 

 faint lines made by a folded area of the coelomic epithelium, 

 bounded in front by a lateral blood-vessel coming from the 

 dorsal vessel. This folded and thickened patch of epithelium 

 extends over the dorsal longitudinal muscles in the posterior 

 half of each segment, and its surface is covered with delicate 

 cilia. If now the strip be examined from the upper surface 

 the folded ciliated area is seen to extend transversely across 

 the middle of each segment, becoming narrower and narrower, 

 and reaching to near the mid-dorsal line. I propose to call 

 this organ the dorsal ciliated organ until we know more 

 about its functions; the portion which lies on the outer sur- 

 face of the muscles may be called the outer limb, and the 

 portion which lies on the inside of the muscles the inner 

 limb. Little more can be seen in the fresh condition ; the 

 exact position and structure of the organ can only be ascer- 

 tained by means of sections. 



For the preservation of Nereis diversicolor hot cor- 

 rosive has, on the whole, given the best results. The worms 

 were chloroformed, then opened up here and there, and the 

 hot preservative poured on them. Hsematoxylin and borax 

 carmine were used as stains. 



In a transverse section through the middle of a segment of an 

 adult N. diversicolor (PI. XXXIV, fig. 5) we see a covering of 

 ciliated epithelium extending on the outer surface of the dorsal 

 longitudinal muscle (figs. 1 and 5, dors. long, m.), and round 

 its ventral border on to the lateral tegumentary blood-vessel 

 (figs. 1 and 5, dors. teg. v.) which communicates with the dorsal 

 vessel (figs. 1 and 5, doi's. v.). This is the outer limb of the 



