The Spermatogenesis of Hydra. 387 
determining factors in the appearance of the testes. When the Hydra 
were placed in the cold water they contracted at first but remained 
so only a short time, when they expanded as usual and resumed 
their normal life. They reduced rapidly in size, becoming emaciated 
more quickly than the animals in control jars at the room temperature. 
H. viridis and H. grisea have been found to be sexually active 
in spring and summer, while H. fusca and H. dioecia are sexually 
active in the fall. It would seem likely that the cause which in- 
itiates sexual reproduction, whatever it may be, is the same in all 
four species, and it was thought possible that spring and fall rains 
might act as the immediate cause. 
Distilled wa tex 
Experiments were tried by placing animals in distilled water 
for varying times and then removing to ordinary pond water. And 
it was observed that animals kept for from six to twenty four hours 
in distilled water and then placed in pond water do develop speedily 
elevations along the sides of the body similar in external appearance 
to young testes. But they disappeared in the course of twelve hours, 
with no consequent developments. The elevation would be readily 
explained by osmosis. The reverse process is also effective in pro- 
ducing these external protrusions, Hydra developing them frequently 
when placed in distilled water. The swellings are not ectodermal 
thickenings, but bulgings of both walls. It is interesting to note 
that they always appear symmetrically on opposite sides of the 
animals as buds tend to appear. 
Change in ion concentration. 
To see if changes in ion concentration would be effective in starting 
the development of sexual organs, a number of solutions in varying con- 
centrations were used. But no results have as yet been obtained, aside 
from demonstrating the extreme sensitiveness of Hydra to the action ot 
= 
solutions, it being necessary to work with 100 solution or still more 
. N IR: 
dilute to prevent immediate death. Thus a 700 NHC! kills H. di- 
oeeia instantly or nearly so. But H. viridis will endure more 
Ao N Kl 
is fatal usually. But individual Hydra differ remarkably, some ani- 
than twice as strong a solution for several hours. 
