648 STUDIES IN GENERAL PHYSIOLOGY 
control material develop into a larva. I noticed only that 
after from seven to ten hours some of these eggs may show 
a beginning of a segmentation which, however, soon ceases. 
This phenomenon seems to be quite common among many 
marine animals. I mentioned in a former paper that O. 
Hertwig had already noticed that it is a common occurrence 
among Arthropods, Worms, and Echinoderms.’ If, however, 
no such aseptic measures against spermatozoa were taken, a 
number of eggs in the control material usually reached the 
trochophore stage. The sea-water used in these experiments 
was sterilized by heating it slowly to a temperature of from 
60° to 80° C. In asmaller number of experiments I used 
sea-water which had gone through a Pasteur (Chamberland) 
filter which, of course, is absolutely impermeable to sperma- 
tozoa.” If the eggs of more than one female were used for 
an experiment, all the eggs were first gathered in one dish, 
thoroughly mixed, and then divided into two lots, one to serve 
as control material and one to be distributed into the various 
solutions. Thus the control material and the material experi- 
mented upon consisted always of the eggs of the same 
females. It goes without saying that the same was the case 
in all my previous experiments on Echinoderms. 
Il. ARTIFICIAL PARTHENOGENESIS CAUSED BY AN INCREASE 
IN THE OSMOTIC PRESSURE OF THE SEA-WATER 
It was natural to try first whether or not the same means 
that cause the parthenogenetic development in Echinoderms 
are also sufficient to bring about the parthenogenetic devel- 
opment of the eggs of Chetopterus. 
First series. — When I received the first material, I at 
10, HERTWIG, Die Zelle und die Gewebe, Vol. I (1893), p. 239. 
2JTn almost all the experiments the sea-water used was sterilized. In a few 
exceptions this precaution was purposely omitted in order to find out whether or not 
the sea-water in the laboratory contained spermatozoa of Chetopterus. This, how- 
ever, was not the case, 
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