NOTES ON THE NATURE OF "ARTIFICIAL PAR- 

 THENOGENESIS" IN THE EGG OF PODARKE 



OBSCURA. 



AARON L. TREADWELL. 



The results obtained by Lillie 1 on the phenomena accompany- 

 ing artificial parthenogenesis in Ch&topterus led me to repeat the 

 experiments, using Podarkc obscitra, with the idea of determining 

 if similar results appear in this genus. I was much interested, 

 also, in the question whether cleavage produced by chemical 

 stimulation bears any resemblance to the normal cleavage ; the 

 latter, in this form, having been carefully followed. 



That Podarkc eggs would develop into ciliated embryos in this 

 way was first determined by Dr. A. W. Greeley, to whose 

 courtesy I am indebted for suggestions in the use of his method. 

 This was treatment for one hour with a mixture of 20 c.c. of a 2^ 

 nKCl solution -f So c.c. of sea water. They were then trans- 

 ferred to sea water, and, after a variable length of time, began 

 to divide. A solution of 22 l / 2 c.c. of 2^> nKCl solution + 77^3 

 c.c. of sea water was also used, but gave less satisfactory results 

 than the other. Through lack of material I did not use any 

 other solutions, and experimented only with unfertilized eggs. 

 This leaves my observations very incomplete, but the results thus 

 far obtained seem worth recording. 



Controls were kept in each experiment. A few of the control 

 eggs after twelve hours or more in sea water passed into what 

 might be termed, by a superficial observer, a "morula" stage. 

 The cytoplasm breaks up into a great many small globules with 

 no trace of nuclear division, the chromatin lying generally in one 

 globule, which is usually larger than the others. These never 

 develop further, and there was never any trace of nuclear cleav- 

 age or ciliated embryos in the control eggs. A similar breaking 

 down into a " morula " occurs in unsuccessful experiments among 



1 F. R. Lillie, Differentiation without Cleavage in the Egg of the Annelid 

 Ch&toplerus pergamentaceus. Archiv f. Entwick. d. Organismen, 14 Bd., T, and 4 

 lift. 



