EXPERIMENTS ON ARTIFICIAL PARTHENOGENESIS 769 



is sufficient to obtain larvae. 1 Eggs as sensitive as this must 

 be carefully handled in two directions if one does not wish 

 to obtain deceptive results. First it is necessary to transfer 

 the eggs from one dish to another in such a way that every 

 mechanical agitation is done away with. This is best done 

 by using pipettes with a wide opening for sucking up and 

 transferring the eggs. The latter manipulations must then 

 be made with the greatest care. The second precaution 

 consists in this, that whenever the experimental eggs are 

 transferred from one solution to another or into sea-water the 

 same mechanical manipulation must be repeated in exactly 

 the same way with the control eggs. In this way it can 

 be determined whether the parthenogenetic development in 

 individual cases is attributable to mechanical agitation, or to 

 other agents which one employs. With these precautions we 

 have made a series of experiments this summer on Asterias 

 eggs and have found up to the present time that, independ- 

 ently of mechanical agitation, only two methods lead to 

 artificial parthenogenesis in starfish eggs. First, the intro- 

 duction of the eggs for from three to twenty minutes into 

 sea-water to which 3 to 5 c.c. of a -^ normal HC1 or some 

 other inorganic acid has been added to each 100 c.c. of sea- 

 water. The second method which was discovered by my 

 pupil, Mr. A. W. Greeley, consists in keeping the eggs, after 

 lying for a certain time in sea-water, on ice for a number of 

 hours. Other methods all gave negative results, especially 

 heating the eggs which Mr. Greeley also tried. Neither did 

 we succeed in obtaining clear results through the abstraction 

 of water from the egg, so that I suspect that in my earlier 

 experiments perhaps, in which I found starfish eggs to 

 develop through an increase in the concentration of the sea- 

 water, mechanical agitation really caused the development. 



1 1 have since found that the eggs of the starfish can develop without any notice- 

 able external cause. [190JJ 



