No. 2.] THE ORIGIN OF THE SEX-CELLS. 223 
budding of the sexual polyp from the nutritive polyp, and 
longitudinal fission playing a somewhat inconspicuous part. 
In a section cutting two male gonophores upon the same 
blastostyle, there was found in two cases ova among the sper- 
matozoa. On one side of the spadix would be an ovum, while 
upon the opposite side, the spermatozoa would appear (PI. I, 
Fig. 7). A great number of serial sections, about one hundred, 
had been carefully studied previously without meeting this state 
of affairs. 
In Podocoryne I found a twin medusa ; this condition has 
also been observed by Grobben. Each medusa seemed to have 
the normal number of tentacles, and to be about the normal 
size. They were attached along the margin between the radial 
canals. 
Amongst the nutritive polyps of Podocoryne, two of normal 
size were found apparently in the act of longitudinal division, 
or of budding; also a nutritive polyp, with a reproductive one 
developing upon either side; thus it seemed possible that 
fission or budding might take place both in the hydroid and 
in the medusa. 
EXPERIMENTAL. 
Under normal conditions the ova were discharged from 9.30 
to 10.30 p.M.; and this necessitated the study of the early 
segmentation stages at night. I tried to make it possible by 
changing the conditions to change the time of deposit of the 
eggs. The Paguri were removed from Littorina shells, leaving 
these with Hydractinia upon them ; they were then placed in 
a dish of salt water which was carefully packed in ice at 8 P.M., 
August 17, 1892. A registering thermometer was placed 
within the refrigerator and found not to have recorded a lower 
temperature than 17.5° C. The dish was removed at 8 A.M., 
August 18. The temperature was 24° at 9.20 A.M.; at this 
time the discharge of ova and spermatozoa from the colonies 
took place; segmentation began in about an hour. 
On August 18, the same colonies that had been exposed to 
the ice on August 17, were exposed to the direct heat from a 
lamp at 8.30 p.M., and ova were laid at 9.15 p.m. These did 
