Il6 ANDREWS. [Vol. V. 



In D. atprca the ova and cell strings in the body cavity 

 present the same general appearance as in D. magna ; but, as 

 already observed, the strings rarely branch, and the ova are 

 actually smaller. 



More numerous measurements in this species give even 

 greater certainty to the conclusion that the ovum and its ap- 

 pendages grow while floating in the body cavity. 



Thus in one individual ova vary from 30 to 325 /x., while the 

 strings measure 150 /x. to 875 //,. in length and 10 to 30 fx. in 

 diameter in extreme cases. Other measurements in various 

 individuals emphasize the increase in diameter of the ovum and 

 the simultaneous growth in length and thickness of the cell 

 strings, though this is relatively less than in the ovum. 



The smallest of these floating ova measured 15 fx., and had 

 two strings 70 and 150/i. long and 11 /z,. wide: the number of 

 cells in these smallest strings is frequently 15, as in the larger 

 species. The strings fall off after the ovum is 300 p. in diame- 

 ter and do not appear to diminish before then, but to drop off 

 intact, though this requires re-investigation. The ovum having 

 lost its strings, increases to 400 /u,., when it is apparently ripe, 

 and has a membrane 2 ll. thick perforated by pores or canals. 

 As strings 400 fi. long frequently have 30 cells, an increase in 

 number as well as growth of individual cells may be assumed 

 to take place during the floating period. The yolk granules 

 of the mature egg do not appear in the youngest stages, but 

 when about 50 ll. in diameter sections show a peculiar vacuo- 

 lation of the protoplasm, indicating a deposition of liquid or 

 solid yolk bodies in the protoplasmic meshwork of the cell 

 body. 



In both species of Diopatra these cell strings may be traced 

 back to the ovaries, which differ but little, though larger, in my 

 sections, in D. cuprea than in D. magna. The size, however, 

 varies much in different individuals and even in different regions 

 of the same individual. 



In either the ovary is a transverse band along the posterior 

 face of a septum, on each side the body, extending from the cav- 

 ity of the parapodium towards the digestive tract, and ending as 

 a protuberant, rounded mass. The ovaries occur in very many 

 somites, and appear to be simply aggregations of peritonaeal cells, 

 or cells projecting freely into the body cavity, with no special 



