228 
as to bring the middle part of the sterile entoderm partly in contact with the sterile entoderm 
near the body wall (fig. 261 C). In Schultze’s and Roule’s figures the S-shape is given, but not 
the direction of the mesogloea. — The mode of origin 
of the testes was especially to be followed in that 
part of the mesentery, which adjoins the bodywall or 
the actinopharynx. Here the mesogloeal capsule of the 
testes-vesiculae is in connection with the mesenterial 
mesogloea, in such a way that the capsule remains 
an open pocket. The surface of the mesogloea is 
Titerrupted above the opening, through which the tails 
of the spermatozoa project outwards, at least across 
the mesogloeal limit, and halfway the thickness of the 
entoderm at the other side of the mesentery. The 
vesiculae numbered 1, 2, 3 in PI. 7 i % 2 show this 
phenomenon, while the fourth is not attained in its 
median plane. — In my opinion the process is as 
follows: at first the primordial germcells are to be 
found in the entoderm on one side of the mesentery, 
viz. that side, which is the narrow unchanged one in 
the fertile mesentery lateron. The mesogloea invaginates below these cells and the germcells are 
found in this invagination, which is the capsule described above, surrounded by the entoderm 
of the other side, which becomes swollen to give room for the capsules. Since there were no 
stadia to be found with an entirely shut capsule, it is probable that the invagination remains 
open during the entire spermatogenesis. When the spermatozoa are ripe, they find an exit 
through the existing opening of the capsule, as is demonstrated by PI. 7, fig. 2. 
The entoderm, which gives rise to the germcells, is situated on the same side as the 
longitudinal musclefibres, higherup in the mesentery. So the testes in their fertile state are found 
on the same side of the mesentery as the transversal musclefibres. I do not know whether 
there are one or several primordial germcells in one single capsule, but the latter case is more 
probable. — The ovaria have the same mode of origin, but now there is always one cell in 
a capsule. Above each ovum the mesogloea is interrupted in the same manner as with the 
testes (cf. PI. I, fig. 7) and the mesentery is also unilaterally swollen. 
The entire polyp, perhaps even the entire colony, is in the same stadium of ripeness. 
Parasites. There are symbiotic Algae to be found in the entoderm of the bodywall and 
even of the mesenteries between the testes. There is also a unicellular parasite of the same 
type as in PI. Ill, fig. 3, but much larger. It is found in the entoderm of the tentacles, near 
the peripheric connective point of tentacle and bodywall. This parasite is oval in shape; the 
longest diameter is parallel with the mesogloea, the short axis of loop, is at right angles with 
the mesogloea. Its plasma is full of vacuoles. The entoderm is not found above the parasite 
(or perhaps in a very thin layer); it is less than 10 p. thick below the parasite, but right 
and left it gets its usual thickness. That side of the parasite, which is in contact with the 
ABC. 
Fig. 261. Schemata of fertile transversal 
mesenteries in horizontal section. 
Black: mesogloea; white: ectoderm and sterile ento¬ 
derm: hatched: fertile entoderm. A the unilaterally fertile 
entoderm is swollen and bends the mesentery S-shaped; 
B hypothetical bilaterally fertile entoderm; C seemingly 
bilaterally fertile mesentery, through unilateral swelling to 
an exceeding degree; usually the mesogloea in the fertile 
part is very inconspicuous. 
