1090 The American Naturalist. [December, 
oviduct and fertilize the eggs before they are laid. To determine 
which of these alternatives was correct a clean jar, holding about 
two liters of water, was taken, and in the water was placed a pair 
of Diemyctylus. ` About half an hour after the mating had 
ceased the water was filtered through absorbent cotton. Adher- 
ing to the upper part of the filter were multitudes of zoosperms. 
This showed that the zoosperms were emitted into the water. 
Another clean jar was then taken and partly filled with water 
from the university water supply, and into it were placed some 
Anacharis and Ceratophyllum that had been in the laboratory all 
winter, and not in contact with Diemyctylus. The female was 
then carefully rinsed in several waters, and finally under the tap, 
to ensure the removal of zoosperms from the surface. She was 
then put into the clean jar with the water plants. It was believed 
that in this way external fertilization would be precluded, and 
that if eggs were laid and developed it would prove internal fer- 
tilization. Commencing the day after isolation, this female laid 
eight eggs in four days (from the oth to the 13th of April). 
In laying the eggs the female would select a place, usually a 
well-leaved part of the Anacharis or Ceratophyllum. This was 
then clasped by the hind legs, and held close to the cloacal 
prominence. The body showed several writhing or serpentine 
movements, the legs were pressed somewhat more closely to- 
gether, and then the female would move away without looking 
around to see whether or not the egg was securely protected. 
When first laid the albumen is quite cloudy, but soon clears up ; 
it is also very adhesive, so that when forced in between the leaves 
it sticks to them and holds them together. It usually took from 
five to ten minutes to lay an egg. Those observed were laid in 
the daytime. 
In case no green vegetation is present, the eggs are laid on bare 
stems (P1. XXIII., Fig. 1) or on stones. The eggs must be laid 
on stones in nature when no vegetation is present, as occurs in 
some parts of Cayuga Lake, where they were found mating. 
After a few days all but two of the eggs showed signs of devel- 
opment, and embryos in various stages were secured and sec- 


