204 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
has been diluted at most with its own volume of sea-water. In this 
way I obtained in some cases as many as 90 per cent of membranes. 
But I must particularly point out the fact that these experiments only 
succeed with the eggs of at most one female in five. In all these cases 
the eggs behave after membrane formation just like those in which 
membrane formation has been evoked by a fatty acid. 
3. This statement of Kupelwieser is correct except in one 
point, namely, in regard to the effect of dead sea-urchin sperm 
upon the sea-urchin egg. {i have made many experiments in 
regard to the effect of the extract of sperm upon membrane 
formation and found that it does not differ from the membrane 
formation by extracts of other tissues. While the eggs of the 
majority of purpuratus are immune against the watery extract 
of dead sperm of foreign species, if they are sensitized by a 
treatment with SrCl,, all or part of the eggs of practically 
every female will form a fertilization membrane,” if some ex- 
tract of dead sperm of a foreign species is added. The extract 
of dead sea-urchin sperm, however, was in all cases absolutely 
ineffective upon the eggs of sea-urchins. In my experiments 
the spermatozoa were killed by keeping them for 20 minutes at 
a temperature of about 50°C. While the extract of foreign 
spermatozoa killed in this way was very efficient, the extract 
of spermatozoa of the sea-urchin killed in the same way was 
absolutely without effect upon the sea-urchin egg. 
We have thus the paradoxical fact that foreign sperm can 
cause membrane formation and in certain cases development 
of the sea-urchin egg, no matter whether the sperm is dead or 
alive; while sperm of the sea-urchin can bring about fertili- 
zation of the sea-urchin egg only if it is alive. The explanation 
of this paradox lies in the statement given in the preceding 
chapter that the lysins of foreign animals can get into the cells 
1H. Kupelwieser, ‘‘Versuche ueber Entwicklungserregung und Membran- 
bildung bei Seeigeleiern durch Molluskensperma,”’ Biol. Centralbl., XXVI, 744, 
1906; Archiv f. Entwicklungsmechanik, X XVII, 434, 1909. 
2 SrCl does not increase the fertilizing power of living sperm. 
