TEE MECHANISTIC CONCEPTION OF LIFE 9 



to which a definite amount of butyric acid (or some other monobasic 

 fatty acid) has been added. If after that time the eggs are brought 

 back into normal sea-water, all form a fertilization membrane in exactly 

 the same way as if a spermatozoon had entered. This membrane for- 

 mation or rather the modification of the surface of the egg which 

 underlies the membrane formation starts the development. It does 

 not allow it, however, to go very far at room temperature. In order 

 to allow the development to go further it is necessary to submit the 

 eggs after the butyric acid treatment to a second operation. Here we 

 have a choice between two methods. We can either put the eggs for 

 about one half hour into a hypertonic solution (which contains free 

 oxygen) ; or we can put them for about three hours into sea- water 

 deprived of oxygen. If the eggs are then returned to normal sea- 

 water containing oxygen they all develop; and in a large number the 

 development is as normal as if a spermatozoon had entered. 



The essential feature is therefore the fact that the development is 

 caused by two different treatments of the egg; and that among these 

 the treatment resulting in the formation of the membrane is the more 

 important one. This is proved by the fact that in certain forms, as 

 for instance the star-fish, the causation of the artificial membrane 

 formation may suffice for the development of normal larvae; although 

 here too the second treatment increases not only the number of larv^, 

 but also improves the appearance of the larvae, as E. Lillie found. 



The question now arises, how the membrane formation can start 

 the development of the egg. An analysis of the process and of the 

 nature of the agencies which cause it yielded the result that the unfer- 

 tilized egg possesses a superficial cortical layer, which must be destroyed 

 before the egg can develop. It is immaterial by what means this 

 superficial cortical layer is destroyed. All agencies, which cause a 

 definite type of cell destruction — the so-called cytolysis — cause also the 

 egg to develop, as long as their action is limited to the surface layer of 

 the cell. The butyric acid treatment of the egg mentioned above only 

 serves to induce the destruction of this cortical layer. In the eggs of 

 some animals this cortical layer can be destroyed mechanically by 

 shaking the egg, as A. P. Mathews found in the case of star-fish eggs 

 and I in the case of the eggs of certain worms. In the case of the 

 eggs of the frog it suffices to pierce the cortical layer with a needle, as 

 Bataillon found in his beautiful experiments a year ago.^ The mech- 

 anism by which development is caused is apparently the same in all 

 these cases, namely, the destruction of the cortical layer of the eggs. 

 This can be caused generally by certain chemical means which play a 



^ This method does not work with the eggs of fish and is apparently aa 

 limited in its applicability as the causation of development by mechanical 

 agitation. 



