10 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
The most remarkable fact, however, is this: that it is 
possible to cause artificial parthenogenesis in eggs which are 
refractory to any other method of artificial parthenogenesis. 
All attempts to cause artificial parthenogenesis in the eggs of 
Cumingia, a marine mollusc, had failed. But Mr. Wasteneys 
and the writer found in 1912 that these eggs can be caused 
to develop into larvae if they are treated with ox blood or 
serum. In order to accomplish this they must first be sensitized 
by a treatment with a solution of SrCl,. The writer had 
previously found that sea-urchin eggs which cannot be caused 
to form membranes under the influence of ox serum will 
do so if they are first treated for some time with a solution 
of SrCl. 
Not only foreign blood but the extract of foreign cells is 
efficient in inducing membrane formation and development in 
the unfertilized egg. Blood of the species to which the eggs 
belong is, however, entirely ineffective for this purpose. This 
is analogous to the fact that foreign ‘“lysins” may destroy the 
cells of an animal while the cells are immune against the lysins 
of their own species. The experiments on artificial partheno- 
genesis indicate that this immunity is due to the fact that the 
lysins are prevented from diffusing into the cells of the same 
species while they can diffuse into the cells of foreign species. 
6. The question may next be raised whether the spermato- 
zoon also effects membrane formation by means of a cytolytic 
substance, a “lysin,” and whether, in that event, it must carry 
into the egg yet another substance besides the lysin for the 
purpose of preventing the disintegration following membrane 
formation. This is what actually appears to be the case. 
Ten years ago I discovered a method of fertilizing the eggs of the 
sea-urchin with the sperm of widely different species, e.g., of 
the starfish. In employing this method, I found that not al! the 
eggs of the sea-urchin which form membranes with (living) star- 
fish sperm develop. Some of the eggs form membranes and 
