684 STUDIES IN GENERAL PHYSIOLOGY 



Echinodernis and Chsetopterus 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 Echinoderrns and ChaBtopterus. 



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 Chsetopterus may develop 

 as far as twelve or sixteen cells. According to Hertwig, not 

 only the eggs of Annelids and Echinoderrns, 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. 1 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- 



i YIGUIER, Comptes rendus de I ' Acadtmie des Sciences, Paris, July 2, 1900. 



