THE BIOLOGY OF THE CELL SURFACE 



parthenogenesis. That he had induced parthenogenesis 

 and had not followed a normally parthenogenetic develop- 

 ment seems to me to be beyond question. Thus without 

 knowing it he was the first to induce parthenogenesis in 

 marine eggs. Evidence may be adduced upon which this 

 judgment is based. 



'-"' In the first line I place Greef's work itself. The observed 

 great difference between the fertilized and the partheno- 

 genetic eggs with respect to the time when they reach first 

 cleavage, points strongly to an experimental induction of 

 development. This was probably brought about by an 

 altered condition of the sea-water. If the eggs were 



crowded, carbon-dioxide was pres- 

 ent in high concentration. At 

 the time of year, the beginning of 

 May, when the observations were 

 made, the water in the vessels 

 containing the eggs most probably 

 rose in temperature, in the absence 

 of any precautions taken against 

 such rise. Or, if the eggs were 

 kept in uncovered vessels, evapor- 

 ation took place. Any one of 



Fig. 32.— Ripe egg of Aster- -i •,• • n n 1 



acanthion ruhens after having these possibilities, all Well-known 



lain two hours in sea-water means for inducing parthenogenesis 



(after Schneider). • ^ c ^ 1 j 



^ in Starfish eggs, would account 



for Greef's results. Schneider in 1883 pictured an tgg of 

 Aster acanthion which after having lain two hours in sea- 

 water showed many asters. This is clear evidence to any- 

 one familiar with this egg that this change is induced by 

 the residence of the egg in sea-water (Fig. 32). 



Secondly, later work on this egg may be considered. In 

 reading O. Hertwig's report on his observations made four- 

 teen years after Greef's, on the egg of Asterias glacialis and 



214 



