The Sexual Phases of Myzostoma. 
241 
fications. and like those of the ventral parenchyma present ali the 
stages in the multiplication and maturation of the male elements. 
Stage 6 a. 1 mm long. Specimens in this stage are found 
like those of the five preceding stages attached to the backs of older 
individiials. The intestinal diverticula now extend into the thin lateral 
edges.of the body and have acquired further ramifiations. 
In the peripheral portions of the ovaries which have now the 
adult form, the triplet-cells are seen breaking away and migrating 
into the body-cavity, which has extended further towards the lateral 
edges of the body along the dorsal surface of the intestinal di- 
verticula. In some of the specimens a few of the oocytes have begun 
their growth while stili in the ovary (compare PI. 12 Fig. 56 o). The 
male reproductive cells are stili increasing in bulk and number. 
Stage 6b. 1 mm long. The specimens have migrated from 
the backs of the older Myzostomes and have attached themselves to 
the disc of the Antedon. Sections reveal almost the same conditions 
as in the specimens of Stage 6a. The body-cavity is becoming larger 
and a few loose triplet-cells are found floating in it near the 
ovary. 
Stage 7. 1 — 1.5 mm long. In this stage there is a further 
enlargement of the body-cavity. The conditions of the female re- 
productive organs may be readily studied in horizontal sections of 
specimens 1.5 mm long, like the sections represented in PI. 11 Fig. 24. 
Here the ovary contains several dividing oogonia [oog] and the triplet- 
cells may be seen breaking away from the irregulär margins of the 
organ. These cell-clusters [o.m] may be traced as they float through 
the ramifications of the body-cavity ia every direction, tili they 
attach themselves to the peritoneal epithelium. In some places they 
have begun to grow into ova together with their accessory cells. 
The appearance of a cross -section of a specimen 1 mm long 
and which, like the preceding specimen, has already settled on the 
disc of the Crinoid is shown in PI. 10 Fig. 19. There is an appre- 
ciable relative decrease in the size and extent of the testes. The 
ova, of which quite a number have taken up their abode in the 
body-cavity, show a tendency to settle on the dorsal peritoneum. They 
very soon become so numerous as to assume polygonal outlines 
from mutuai pressure. None of these ova have as yet reached 
maturi ty. Düring their growth the peritoneal epithelium grows in 
between them and appears to surround them with follicles of flattened 
cells. These foUicular partitions may in some cases arise from the 
