552 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
figs. 47, 48) produce the mature organs by the division of the cells 
lying toward the center (fig. 48) have been repeatedly mentioned 
by other workers. When the testis first becomes distinct as such 
(fig. 47), the cell outlines cannot be satisfactorily made out except 
in the dividing or reconstructing cells (fig. 48) toward the center. 
It is the same in the case of the incipient yolk glands, but these 
from the time they can be distinguished as yolk glands are found 
with two kinds of nuclei (pi. 16, fig. 44). In the yolk gland rudi¬ 
ments it is as though the cytoplasm of the smaller cells were making 
a stroma in which to swing the large nuclei. A similar condition i& 
noticed in the adult ovary (pi. 17, fig. 52). At the time the testes- 
are distinguishable as many spheres of cells (pi. 16, figs. 47, 48) 
lying along on either side of the body (pi. 18, fig. 53) the ovary can 
be distinguished just in front of the most anterior testis and is quite 
characteristic in its appearance (pi. 17, fig. 49). I believe that the 
ova arise from formative cells though they show their characteristic 
nuclei so early that their origin is not as evident as in the case of 
the testes and yolk glands (pi. 16, fig. 46). At the stage shown in 
figure 49 (plate 17) there are already, among the young ova, smaller 
nuclei {ctn) and these I consider homologous with the smaller nuclei 
found throughout the connective tissue framework of the adult ovary 
(pi. 17, fig. 52, ctn). 
The development of the different elements of the reproductive 
system in relation to one another is shown by the diagrammatic 
figures, 53, 54, 55 (plate 18), 56 (plate 19). Figure 53 represents a 
stage at which the ovaries (o) and the testes {t) can be distinguished. 
There is as yet no sign of any atrium. At a stage slightly older than 
the above (fig. 54) there appears in the region of the genital atrium 
a cleft in the parenchyma (pi. 19, fig. 57 ; pi. 16, fig. 45). This is 
preceded by a noticeable collecting of parenchyma nuclei at this 
spot (pi. 16, fig. 45, n), but I have not found stages which establish 
the origin of these from formative cells. Lining the cleft, an epithe¬ 
lium is formed. In this stage there is present along the line of the 
future oviduct, a long cord of cells a portion of which is shown in 
figure 44 (plate 16). This extends from the region of the ovary 
backward above the nerve cord past the beginning of the atrium 
and well down into the tail. There are at this time no other cell 
cords of this sort in any part of the worm except close alongside 
and connecting with this main stem in places where it is double for 
