1901,] NATURAL SCIENCES OF PHILADELPHIA. 725 



hasty, aiid the question has arisen in my mind, could Burger have 

 mistaken a regeneratin<)j posterior end for a true caudicle ? 



Without wishing to criticise the statement of this distinguished 

 investigator, it seems probable that a further investigation of the 

 caudicles of the European species of Mlcrura and Cerebratulus 

 will result in an agreement with the structure of the American 

 species. 



III. Parasites. 



A monocystid Gregarine in its adult form is frequently present 

 in the middle intestine of Zijgeupolla. Large cysts, surrounded 

 by a thick cuticle and containing various developing stages, are also 

 found in the iutestiue. From their proximity to the adult Grega- 

 rines, and from their resemblance to the stages figured by different 

 authors, it seems likely that these are Gregarine cysts. Outside 

 of the cyst, in the lumeii of the intestine, are small amoeboid 

 masses, resembling some of the stages within the cyst. These 

 amoeboid masses also penetrate between or into the cells of the 

 intestinal wall and probably into the gonads. 



In some living specimens large white spots may be noticed 

 among the gonads, fig. 6. They are so large that they are easily 

 seen with the unaided eye. They appear stalked, like the ova, and 

 have a large nucleus with one or more nucleoli. Fig. 56, a hori- 

 zontal optical section drawn from life, shows one of these structures 

 in a gonad together with several ova. In life the cytoplasm appears 

 denser and darker than that of the small ova, and the conclusion 

 first reached after studying these living bodies was that they were 

 the oldest, nearly mature ova. 



The examination of sections in which these large bodies are 

 present has shown that the first conclusion was erroneous and 

 has proved that they are the encysted stages" of some parasites 

 within the cytoplasm of the ovum. Fig. 60 is a transverse section 

 through the body wall and the wall of the gonad, showing the 

 cyst, surrounded by egg cytoplasm, ey., and attached to the 

 gonad wall, Gon. W. The cyst is surrounded by a striated cuticle, " 

 CtL, and outside the cuticle is a delicate membrane staining like 

 the cell membrane. In the cytoplasm of the base are two egg 



''' The reference line from CtL, fig. 60, only extends as far as the egg mem- 

 brane, instead of to the cuticle within. 



