334 
SAMUEL RITTENHOUSE 
DEHISCENCE 
The eggs are discharged at about five o'clock in the morning. 
The ectodermal epithelium of the ovaries becomes ruptured, in 
fact broken down; and by the movements due to the muscular 
contractions of the manubrium the eggs are set free into the cavity 
of the sub-umbrella. Then by the rhythmic contractions of the 
bell they are forced out of the bell cavity into the water outside. 
While the eggs are being laid the medusa remains at one spot, 
unless disturbed, and keeps up a continuous and rhythmic con- 
traction and expansion of the bell and proboscis. Thus as the eggs 
are liberated, one, two, or three at a time, they are almost imme- 
diately passed out with the ejection of the water from the bell 
cavity. The process of dehiscence lasts for a few minutes during 
which the medusa remains at the bottom of the aquarium. All 
the mature eggs are discharged without intermission in the process, 
unless the medusa is disturbed. In that case it frequently swims 
to another part of the aquarium and in a short time commences 
to discharge the eggs again. The eggs in the ovaries of Stomotoca 
apicata are usually all deposited at one time. Occasionally a few 
immature ones are left in the ovaries after the process of dehis- 
cence. Whether these mature and are laid at a later time, or 
whether they are reabsorbed I am unable to decide. 
As stated above, the eggs are laid at about five o'clock a.m 
On several occasions I observed the process of dehiscence and 
found that the time was always practically the same. Some 
medusae were watched all night, July 14. At five o'clock in the 
morning they began to lay their eggs. They all began at about 
the same time and all the eggs were discharged within fifteen or 
twenty minutes. The time when the medusae are captured and 
put into the aquarium does not seem to have any influence on the 
period of dehiscence. I have taken them in the tow at nearly 
all hours of day and night, and never had them to deposit their 
eggs except at five o'clock in the morning. 
