228 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
suggest what may be the nature of the second factor in the 
spermatozoon. The ‘‘lysin’’ of the spermatozoon serves for 
the production of membrane formation. The second factor 
serves to turn the development into the right direction by the 
suppression of the tendency to disintegrate.! 
2. A second proof for the fact that the spermatozoon causes 
the development of the egg by two agencies, one of which causes 
merely membrane formation, is contained in the following facts. 
The eggs of S. franciscanus can be more easily caused to form 
membranes than the eggs of S. purpuratus. I found in 1908 and 
1909 that if we add living spermatozoa of the shark or of fowl] 
to such eggs, the eggs form membranes.” In the case of the 
spermatozoa of the shark it was possible to wash them first 
repeatedly in sea-water and thus free them from all blood or 
lymph. Nevertheless, the eggs of S. franciscanus formed ferti- 
lization membranes upon contact with the living spermatozoa 
of the shark. Such eggs, when left to themselves, began to 
segment but very soon disintegrated. If they were, however, 
treated afterward with a hypertonic solution they developed 
into larvae. The explanation of this fact is that the living 
heterogeneous spermatozoon upon contact with the egg gives 
off to the latter the membrane-forming substance, without 
supplying the corrective effect. 
A third proof lies in the fact, mentioned in a previous chap- 
ter, that the watery extract of foreign sperm calls forth the mem- 
brane formation in the same way as butyric acid does without 
supplying the second corrective factor. 
3. I have tried in vain to separate in the same way the 
membrane-forming substance from the living sperm of the sea- 
1In order to test this idea further I asked Dr. Elder to make a cytological 
examination of these eggs. He found that when only a few eggs of S. purpuratus 
which had formed membranes developed into larvae a small percentage showed 
the sperm nucleus; while the other eggs had no sperm nucleus although they had 
formed a membrane. 
2 Loeb, Address at the International Congress of Medicine, Budapest, 1909; 
reprinted in The Mechanistic Conception of Life, 1912. 
