No. i.] REPRODUCTIVE ORGANS OF DIOPATRA. WJ 



membranous investment. 1 Each mass surrounds a large blood- 

 vessel and its lateral branches, and may be regarded as consist- 

 ing of two portions, the one applied to the septum, a densely 

 aggregated collection of nuclei in a protoplasmic matrix; the 

 other projecting into the body cavity freely, a festoon-like collec- 

 tion of cell strings or necklace-like loops, each capped by an 

 ovum at its most protuberant, free part (Fig. 5). 



These projecting loops are most abundant at the largest part 

 of the organ, nearest to the digestive tract, and are identical 

 with the smallest cell strings found floating freely in the body 

 cavity. In D. cuprea the ova at the ends of the loops measure 

 11 to 16 /x. in preserved specimens, and are thus as large as the 

 smallest ones found free in the body-cavity liquid. In D. magna 

 the largest ovarian ova measured only 22 p., or half the dimen- 

 sions of those found free in the body cavity ; but I have no 

 doubt sufficient material would show identity in size, as there 

 is in all other respects, between the smallest free ova and those 

 still attached to the ovary. 



The smallest ova in the strings are but little in excess of the 

 other string cells in diameter, and form but slight departures 

 from the general shape and structure of the cells of the entire 

 series (Fig. 6). Thus from a series of nearly identical cells there 

 is formed by great relative growth of the central one a condition 

 in which the latter becomes distinguished as a large ovum with 

 the lateral parts of the string now attached to one side of it as 

 two cellular appendages. The cells of the loop are largest 

 nearest to the central ovum, and diminish towards the two ends 

 attached to the ovary. At first attached on opposite poles of 

 the ovum, the two halves of a string or loop become gradually 

 carried around on to one side by the unequal increase or growth 

 of the surface of the ovum, the side turned away from the ovary 

 projecting into the body cavity at the apex of the loop, growing 

 more than the opposite side. In attempting to follow the cell 

 strings back to their first appearance in the ovary, we find the 

 cell walls no longer visible in that part spoken of as the solid 

 matrix near the septum, but there the nuclei are small and 



1 The nephidium in D. cuprea opens by a wide, transversely elongated funnel, pro- 

 jecting anteriorly from the septum and separated by it from the ovary of the next 

 posterior somite. It passes laterally in the septum as a tube opening ventrally at the 

 base of the parapodium. 



