HISTORY OF ARTIFICIAL PARTHENOGENESIS 49 



the egg of the frog can be induced to develop parthenogeneti- 

 cally by a puncture with a needle. It is not impossible that in 

 the experiments mentioned here on silkworms also a rupture 

 or puncture of the surface layer was the cause of the develop- 

 ment. 



TichomirofFs researches caused Dewitz 1 to interpret as 

 parthenogenesis a previous observation of his upon frog eggs. 



When I was working in the spring of 1885 under Professor Zuntz ^-r 

 in the pl^siological institute of the agricultural college in Berlin, I 

 placed, for certain reasons, unfertilized eggs of Ranafusca in a solution 

 of corrosive sublimate. The next morning, to my astonishment, 

 I found them swollen and segmented. In some of the eggs only one 

 division had taken place, in others more than one; in some the cleavage 



was irregular, but in very many perfectly normal Moreover, 



this occurred just as well if the eggs remained lying in the sublimate 



as also when they had remained there only a few minutes 



Hence it can be concluded that sublimate exerts a stimulus which causes 

 the first division. 



There can be no doubt that the last conclusion is incorrect. 

 What Dewitz observed was obviously a coagulation phenome- 

 non which led to a wrinkling of the surface of the egg and in 

 which the essence of cell division, viz., nuclear division, was 

 absent. This was afterward pointed out by Roux. 2 



In the eighties and nineties, the attention of morphologists 

 was directed to the finer processes of nuclear and cell division. 

 This line of work yielded to the domain of facts in which we 

 are interested here, the observation that the unfertilized eggs of 

 certain sea-urchins may show the beginning of nuclear or even 

 a cell division if they remain long enough in sea-water. The 

 first systematic observation on this count probably originated 

 from Richard Hertwig. 3 



1 J. Dewitz, "Kurze Notiz ueber die Furchung von Froscheiern in Sublimat- 

 losung," Biol. Centralbl., VII, 93, 1888. 



2 W. Roux, Gesammelte Abhandl., II, 432. 



3 R. Hertwig, "Ueber die Entwicklung des unbefruchteten Seeigeleies," 

 Festschrift fur Gegenbaur, Leipzig, 1896. (Hertwig had already reported on these 

 observations in the German Zoological Association in 1892.) 



