188 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
him is especially interesting: “A new piece of silver money, 
which had been specially cleaned before use, was put into 
26 c.c. of sea-water which contained unfertilized eggs of Echinus. 
Fifteen minutes later I noticed in eggs which lay close to the 
silver the formation of membranes. An hour later membranes 
were formed in some eggs which were not so close to the silver.’’! 
The observation by Bohn that radium may induce arti- 
ficial parthenogenesis probably belongs in the same chapter.? 
I believe that in all these cases we are dealing with cytolytic 
effects. The fact shown in chap. xii, that complete cytolysis 
of the egg by saponin raises the rate of oxidations in the ferti- 
lized egg to the same rate as fertilization, makes it clear that the 
cytolysis of the surface layer is the essential part in the causation 
of development in the egg. + 
9. In conclusion, we will briefly touch upon the mechanism 
of cytolysis. In the case of the chorion of the eggs of molluses 
and annelids it can be directly observed that substances like 
saponin and benzol exert an influence that causes swelling and 
liquefaction. This swelling, or absorption of fluid, and the 
clarifying of cell-contents that were previously opaque, are 
typical of cytolysis. Many authorities follow K6ppe in assum- 
ing that cytolysis depends upon the solution of the hypothetical 
lipoid membrane of the egg; it should, however, be stated that 
the fertilization membrane of the eggs is insoluble in benzol, 
or in any other lipoid-solvent. 
Von Knaffl has developed another conception of the mech- 
anism of cytolysis, which I shall quote verbatim. 
It can be regarded as certain that protoplasm is rich in lipoids, 
and that any chemical or physical stimulus which produces a lique- 
faction or solution of the lipoids of protoplasm, causes the egg to eyto- 
lyze owing to the fact that the protoplasm, being now free from lipoids, 
takes up water, and swells. This leads in many cases to the bursting 
of the membrane. 
1 Herbst, Mitteil. d. Zool. Station zu Neapel, XVI, 445, 1904. 
> G. Bohn, Compt. rend. Acad. d. Sc., CXXXVI, 1085, 1903. 
