History of Artificial Parthenogenesis 55 



order to see whether it were not possible to cause unfertihzed 

 sea-urchin eggs to develop into larvae by altering the constitu- 

 tion of the sea-water. My chief idea was that it must take 

 place by means of hydroxylions or of hydrions. For earlier 

 experiments had shown that an addition of acid to sea-water 

 retards the development of sea-urchin eggs.' 



Moreover, it was conceivable that the alkali of the sea- 

 water or the formation of carbonic acid in the unfertilized eggs 

 was itself the cause that they began occasionally to divide 

 spontaneously after a prolonged sojourn in sea-water. So I 

 then tried whether it was possible to cause the development 

 of the unfertihzed sea-urchin egg into a larva by means of alka- 

 lies or acids.'' My later investigations have shown that I 

 was right in this idea, but through a curious accessory circum- 

 stance I did not at that time succeed in my object. For I 

 was then of the opinion that only the hydrions are of impor- 

 tance in the physiological effect of acid, and hence I used only 

 strong mineral acids. I have since found that in this case only 

 the weak acids are effective. Had I used fatty instead of 

 mineral acids, the development of this branch of biology would 

 have been shortened by five years. 



On the other hand the experiments on the addition of MgCls 

 to the sea-water were successful, provided that at the same 

 time the osmotic pressure of the sea-water was raised.' Unferti- 

 lized sea-urchin eggs which had been exposed for two hours to 

 such a mixture developed afterward into larvae, some of which 

 reached the normal pluteus stage. In this way the first step 

 was taken which rendered possible the systematic analysis of 

 the nature of the process of fertilization. For we possess only 



' Loeb, " Ueber den Einfluss von Sauren und Alkalien auf die embryonale 

 Entwicklimg und das Wachstum," Archiv /. Entwicklungsmechanik, VII, 631, 1898. 



= Loeb, Am. Jour. Physiol., Ill, 434, 1900. 



' Loeb, "On the Nature of the Process of Fertilization, and the Production 

 of Normal Larvae (,Plutei) from the Unfertilized Eggs of the Sea-Urchin," Am. 

 Jour. Physiol., Ill, 135, 1899. 



