No. 2.] THE ORIGIN OF THE SEX-CELLS. 225 
had not retarded their action, as their action was the same as 
with the others, which had been removed from the ice at the 
‘same time, and exposed to the light. 
My experiments lead me to formulate the opinion that the 
ova and spermatozoa are ripened and ready for expulsion about 
10 o'clock p.m.; and that by chilling the whole colony for a 
sufficient length of time before this period, it is possible to 
delay the time of deposit. 
Experiments were tried in order to learn just when the ova 
were fertilized. The male and female colonies placed upon ice 
were kept separate over night. Artificial fertilization was then 
tried by adding some water from the male colonies containing 
spermatozoa to the ova of the female colonies which had been 
deposited, but no segmentation followed excepting in a few 
cases, where there was a beginning of the first furrow. In 
another experiment, the male and female colonies were separ- 
ated immediately upon removal from the ice, and the water 
changed before there was evidence of the ova being deposited, 
yet they segmented. Therefore it is to be supposed that the 
spermatozoa either fertilize the ova just as they are about to 
escape, or at once upon their discharge, probably before they 
have sunk to the bottom of the dish; yet it is possible by 
microscopical examination to see an ovum surrounded by 
spermatozoa, after it has so settled. 
At Wood’s Holl on June 25, the Hydractinia which were 
first collected, showed a much larger percentage of male 
colonies than of female ones. During the latter part of July, 
and August, when the temperature of the water had risen, and 
the conditions for nourishment were more favorable, there was 
an excess of female colonies. There was not sufficient data 
obtained to prove conclusively that temperature and nutrition 
influenced the determination of sexes, but the difference in 
‘their proportion with regard to these conditions suggested 
that temperature or nutrition were the causes for this 
differentiation. 
The work of Driesch upon Echinus, and Roux upon Rana, 
suggested the following experiments upon Hydractinia. In 
several instances at the two-celled stages, the blastomeres were 
