Il8 EDWIN LINTON. 



placed in corrosive-acetic and afterwards sectioned. The sections 

 show an immense number of sporocysts (Fig. 5). For the most 



, -t® ^ J^y^s' .--2. ' 



Fig. 5. Transverse section of Hydroides dianthus showing sporocysts embedded 

 in the body wall, a, intestine. 



part they are distributed ventrally in the inner portion of the 

 body wall, although a few lay among the muscles near the 

 exterior, and a few in the epidermis. If I interpret the sections 

 correctly, the sporocysts escape from the ventral side of the 

 serpulid, where the body wall is comparatively thin, and where 

 the sporocysts are in greatest numbers. 



There is considerable variation in the size of the sporocysts. 

 The largest noted was 0.70 millimeter in length and 0.28 milli- 

 meter in diameter; the smallest 0.17 in length and o.io in di- 

 ameter. In like manner the cercariae varied in length, but the 

 length of 0.12 millimeter for the anterior portion, and 0.36 for 

 the tail, or 0.48 millimeter for the whole length, is not far from 

 the usual length of a mature cercaria. One cercaria, living, had 

 the following dimensions : Length of body 0.17 millimeter, breadth 

 0.04; length of tail 0.52, breadth 0.02. 



What were interpreted to be striated muscle fibers were 

 noticed in the tails of living cercariae (Fig. 3). These fibers 

 extend diagonally backward and inward from the exterior to 

 the median line. They were about 0.0017 millimeter in diameter, 

 and what appeared to be cross striations were plainly visible 

 with a Zeiss D objective. Under an oil immersion lens their 

 resemblance to striated muscle was evident. 



