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. 1 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 a smaller number of experiments I used 

 sea-water which had gone through a Pasteur (Chamberland) 

 filter which, of course, is absolutely impermeable to sperma- 

 tozoa. 2 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. 



II. 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 Chsetopterus. 



First series. When I received the first material, I at 



1 O. HEETWIG, Die Zelle und die Gewebe, Vol. I (1893), p. 239. 



2 In 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 Cheetopterus. This, how- 

 ever, was not the case. 



