L. V. HEILBRUNN. 



Length of Exposure to i Per 



Cent. Egg Albumen. Segmentations. 



30 minutes 55/ioo 



66 48/100 



118 SO/TOO 



233 6/100 



The results gained with the endosmotic method used alone, 

 are never as good as those which can be obtained with the ex- 

 osmotic method. Neither are the per cents, of segmentation as 

 high, nor is the degree of development attained as great. In 

 spite of the fact that Loeb ascribes to hypertonic solutions a 

 mere correcting effect, it is I think a noteworthy fact that no 

 method of artificial parthenogenesis yet tried on the Arbacia 

 egg, is truly effective, unless at some stage of the process it 

 requires a hypertonic solution. In connection with this point, 

 I made a number of experiments to test the butyric acid-KCN 

 method which Loeb found so effective for Stronglocentrotus. 

 I was at the time convinced that the method was essentially 

 the same as Delage's acid and alkali method (Delage '07), and 

 I tried to find if NaOH could not be substituted for the KCN, 

 in other words if the correcting action of the latter was not due 

 solely to its alkalinity. In no case, however, was I able to get 

 any results either with KCN or NaOH as a "correcting agent" 

 after butyric acid treatment. Indeed recently Loeb ('136) 

 has pointed out that the method is not suited for the Arbacia egg. 



The question now arises if the two methods of producing 

 segmentation, the one endosmotic, the other exosmotic, have 

 anything in common. As a result of my experiments, I find 

 that both methods produce a gelatinization or coagulation 

 within the egg. 1 



Most biologists believe that the mitotic spindle is a con- 

 densation or coagulation product, and there is excellent support 

 for this view. Hence any initiation of development must soon 



1 In the test-tube, gelatinization and coagulation of proteins are apparently 

 quite different phenomena, the former converting the entire mass into a jelly, 

 the latter resulting in a separation of a precipitate. But in the small field of 

 action of a sea-urchin egg, it would not be so easy to distinguish between the two, 

 for the entire egg is smaller than a single flake of the usual precipitate. Moreover, 

 even in the test-tube coagulation is usually preceded by a stage strictly comparable 

 to gelatinization; the entire mass becomes opalescent and assumes a greatly 

 increased viscosity; only later does the precipitate appear. 



