No. 395.] PENNARIA TIARELLA McCRADY. 869 
vations upon the Medusz will be necessary after they become 
free, in order to ascertain whether a true mouth is formed. In 
the layers of the mature Medusa there is scarcely any cellular 
structure evident. The cytoplasm in the cell has disappeared, 
and the only structural feature present is a round body, which 
stains very deeply and looks as if it might be a nucleus in a 
very reduced condition. The chymiferous tubes have entirely 
disappeared except where the sense organs are found. That 
these tubes are functional in some of the earlier stages seems 
reasonably sure, because food has been found in them which 
was of the same character as that found in the hydranth. The 
connection between the hydranth and the Medusa becomes 
reduced with the growth of the Medusa, and finally breaks 
when the conditions are favorable. 
The Medusze of Pennaria seem to be in a degenerate condi- 
tion, and in a sense occupy an intermediate stage between the 
free-swimming Medusæ and those that have lost all resemblance 
to this stage and are never free, as in Clava, Eudendrium, and 
others. The two most important reasons for thinking the Pen- 
naria Medusz degenerate are: first, the change which the chy- 
miferous tubes undergo; and, second, the fact that there is no 
apparent mouth or circumferential canal. While the evidence 
is not conclusive, yet it is very suggestive and may throw some 
light upon other forms, 
OOGENESIS. 
While considering the development of the Medusa, it was 
stated that the cells originating from the ectoderm, and which 
filled up the cavity between the manubrium and the bell, were 
destined to give rise to the reproductive elements. 
If the cells are studied in such stages as are represented 
by Figs. 3 and 4, they will be found to be large and to pos- 
sess large prominent nuclei. These cells continue to enlarge 
for a time, during which the cytoplasm becomes denser and 
more granular close to the nuclei. These may all be consid- 
ered primitive ova at this stage. Five or six of these, at the 
most, are all that may mature into eggs. If the various cells 
