10 



The Mechanistic Conception of Life 



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 

 larvae, but also improves the appearance of the larvae, as 

 R. Lillie found. 



The question now arises, how the membrane formation 

 can start the development of the egg. An analysis of the 



Fig. 8 



Fig. 9 



Fig. 8. — Blastula. First larval stage of the sea-urchin egg. At the surface 

 of the cells cilia are formed and the larva begins to swim and reaches the surface 

 of the water. 



Fig. 9. — Gastrula stage. The intestine begins to form and the first indica- 

 tion of the skeleton appears in the form of fine crystals. 



process and of the nature of the agencies which cause it 

 yielded the result that the unfertilized egg possesses a super- 

 ficial 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 destruc- 

 tion of this cortical layer. In the eggs of some animals this 

 cortical layer can be destroyed mechanically by shaking the 



