Tlie Sexual Phases of Myzostoma. 
239 
karyokinetic figures are often poorly preserved and periodic in their 
appearance. 
Towards the free periphery of the ovarian mass the cells are 
already arrang-ed in triplets, each of which consists of an oocyte 
with a smaller accessory cell on either side. An examination of 
Fig. 23 a~g will show that the stages in the setting free of these 
triplets, their attachment and growth agree very closely with the 
corresponding stages of M. cirriferum. The accessory cells are as- 
similated by the growing oocyte, or ovum in the same manner. The 
last reranants of these cells are traceable only to the deeply staining 
stage of the ovum (Fig. 23/). In the earlier stages (Fig. 23 c — f) 
several irregulär and deeply staining granules are found scattered 
through the cytoplasm especially towards the poles. These may be, 
for ought that can be determined to the contrary, the disintegrating 
masses of chromatin belonging to the nuclei of the accessory cells. 
The granules are not seen in the stage represented in Fig. 23^. 
When a series of individuals of M. glahrum of difFerent sizes 
was carefully sectioned and Studie d the following facts in the growth 
and structure of the reproductive organs were ascertained: 
Stage 1. 0.175 mm long. There is a distinct and 
rather spacious body-cavity in this stage. The diverticula 
of the intestine are very short, however, being mere hollow buds. 
In the region of the ovary there is a small a c cumula tion 
of peritoneal cells (young oogonia) which are indis- 
tinguishable in appearance from the spermatogonia, 
a few of which are found in the ventral parenchyma. 
These spermatogonia are not always clearly distinguishable from 
other non-sexual cells which are still relatively large and have a 
somewhat embryonic appearance. 
Stage 2. 0.25 mm long. The body-cavity has grown 
smaller, the gut -diverticula somewhat longer. This decrease in 
the extent of the body-cavity in this stage is to be attributed to the 
proliferation of the spermatogonia which, I believe, first arise from 
the Peritoneum lining the floor of the body-cavity and thence pro- 
liferate downwards into the ventral parenchyma between the in- 
sertions of the parapodia. The masses of spermatogonia thus formed 
appear to push up against the floor of the body-cavity and tend to 
obliterate its lumen. Many spermatogonia are dividing in this stage, 
but the majority are in the resting stage. A very few spermatocytes 
have been formed and have begun to divide, but none of the male 
