132 The Mechanistic Conception of Life 



namely, first the artificial causation of the membrane formation 

 and second the subsequent short treatment of the egg with a 

 hypertonic solution; (or a longer treatment with an isotonic 

 solution free from oxygen or containing KCN). 



We may add that these observations do not hold good for 

 the sea-urchin egg only. Similar observations were made on 

 the eggs of annelids (Polynoe) and of star-fish (Asterina). 

 In Polynoe and star-fish the artificial membrane production is 

 often sufficient to allow the eggs to develop into larvae. But 

 the number of eggs which reach the larval stage and the type 

 of segmentation is improved if the eggs are treated subsequently 

 with one of the above-mentioned methods, as R. Lillie found for 

 Asterias and I for Polynoe. The experiments on annelids and 

 star-fish, therefore, confirm the fact, that the calling forth of 

 the membrane is the essential feature in formative stimulation 

 and that the subsequent treatment of the eggs with a hyper- 

 tonic solution (or an isotonic solution free from oxygen) has 

 merely a corrective effect; it probably coimteracts a secondary 

 detrimental effect connected with the membrane formation. 



Ill 



We will now try to gain some insight into the mechanism of 

 these two agencies. How can the fatty acid cause the formation 

 of a membrane? In order to get an answer to this question 

 we must find out whether there are other agencies which 

 act hke fatty acids. It was noticed that all the agencies 

 which cause cytolysis also cause membrane formation, namely, 

 first the specifically cytolytic agencies like saponin, solanin, 

 digitalin, bile salts, and soaps. Experiments with these agencies,, 

 especially with saponin, solanin, and digitalin, yielded a curious 

 result. If the unfertilized eggs are put into a weak solution of 

 saponin in sea-water we notice as the first effect on the eggs 

 the formation of a fertilization membrane. Then ensues a pause 

 of sometimes several minutes and after this pause a sudden 



