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 SrCl2, 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 



1 H. Kupelwieser, "Versuche ueber Entwicklungserregung imd Membran- 

 bildung bei Seeigeleiern durch MoUuskensperma," Biol. Centralbl., XXVI, 744, 

 1906; Archiv f. Entwicklungsmechanik, XXVII, 434, 1909. 



2 SrClj does not increase the fertilizing power ot living sperm. 



