172 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
the peritoneal epithelium. In view of the widely differing results 
in the observations of various investigators upon this muscle layer, — 
they have been reviewed by Ludwig ('89—92, p. 191), — it may 
be well to add that in Thyone, as in Caudina, I have found only 
circular fibers, whereas in Synapta Girardii Pourtalés there is a 
layer of longitudinal fibers, beneath which occasional circular fibers 
occur, that are by no means numerous enough to form a distinet 
layer. My observations upon Caudina and Thyone agree with 
those of Jourdan upon Cucumaria and Phyllophorus, as well as with 
those of Hérouard; the species of Synapta which I have examined 
differs from S. digitata, as described by Hamann, in that it lacks 
a continuous layer of circular muscle fibers. 
c. The connective-tissue layer consists of closely laid fibers and 
stellate cells. The most of the fibers run in a longitudinal direction, 
and form in some cases a close but extremely thin weft, immediately 
beneath the muscle layer. It is in the spaces between the fibers 
of connective tissue that the homogeneous blood plasma circulates. 
Upon opening a tubule one finds longitudinal folds of tissue (Zac. 
oa.) extending into the lumen (Plate 6, fig. 83). There are often 
two of these in the same part of the tubule, but on opposite sides; 
or there may be in some tubules several neärly parallel folds pro- 
jecting from the inner wall. This loose tissue forms a part of the 
lacunar system, and in its interstices there is contained a homo- 
geneous blood plasm. Flat cells of the internal epithelial layer 
enclose these haemal sinuses, and scattered stellate cells stretch 
across the lacunae. No calcareous bodies are to be found in this 
connective-tissue layer, 
d. The internal epithelium requires a more extended account 
than has been given of the other layers. I shall describe first the 
conditions in the female and then those in the male. 
Ovaries and oögenesis. In the youngest individuals which I 
have succeeded in obtaining, the tubules of both sexes were just 
beginning to branch. At this stage of development the cells of 
the germinal epithelium are attached in irregular masses to the inner 
wall of the egg tubules, These masses have probably resulted from 
the division of the primitive sexual cells, Already the future ova 
are to be distinguished by their larger size from the cells destined 
to form around them a follicle (Plate 6, fig. 83). The two kinds 
of cells resemble each other in having relatively large spherical, or 
slightly oval, nuclei, containing numerous small chromatic bodies 
