684 STUDIES IN GENERAL PHYSIOLOGY 
Echinoderms and Chetopterus possible. In plant lice the 
effect is of the same kind, only in the opposite direction. 
I have read somewhere the statement that Artemia salina 
is parthenogenetic, while Branchipus is not. Branchipus is 
a fresh-water Crustacean which, if raised in concentrated 
salt solutions (salt lakes), becomes smaller and undergoes 
some other changes. In that case it is called Artemia. If 
Artemia is parthenogenetic while Branchipus is not, it would 
mean that the unfertilized eggs of the Branchipus cannot 
develop in fresh water, while they are able to develop in 
solutions of much higher osmotic pressure. This would be 
identical with our observation on the artificial parthenogenesis 
of Echinoderms and Cheetopterus. 
As I have mentioned in a former paper, O. Hertwig makes 
the statement that the unfertilized eggs of a number of marine 
animals which deposit their eggs in sea-water begin to de- 
velop after a number of hours, but do not develop beyond the 
first cleavage stages. Arbacia eggs reach the two-cell stage 
in about twenty hours; the egg of Cheetopterus may develop 
as far as twelve or sixteen cells. According to Hertwig, not 
only the eggs of Annelids and Echinoderms, but also those 
of certain Crustaceans show this peculiarity. I have men- 
tioned in a former paper the observation made by Janosik 
that in the ovary of mammals occasionally eggs are found in 
the process of cell-division. We shall make use of these 
facts in the next section. 
I finally wish to say a few words concerning experiments 
published by Mr. Viguier of Africa, who maintains that the 
eggs of Arbacia, Toxopneustes, and other sea-urchins are 
naturally parthenogenetic.’ It would contradict neither my 
experiments nor my views if his statement were correct, as 
in all my papers I have assumed that these and many other 
(if not all) eggs have a tendency to develop parthenogeneti- 
1 VIGUIER, Comptes rendus de l’ Académie des Sciences, Paris, July 2, 1900. 
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