ON SOME FACTORS GOVERNING THE PERMEA- 

 BILITY OF THE EGG MEMBRANE 

 BY THE SPERM. 



H. H. NEWMAN. 



In the summer of 1903 Loeb 1 succeeded, by slightly increas- 

 ing the alkalinity of sea water, in fertilizing the eggs of the sea- 

 urchin (Strongylocentrotus purpuratus] with the sperm of the 20- 

 rayed starfish, with that of Asterias and with that of the Holo- 

 thurian, Cttcumaria, while at the same time the eggs were ren- 

 dered immune to their own sperm. 



The question arose as to the character of the change in the 

 egg or in the sperm that makes the former sometimes permeable 

 to its own sperm and impermeable to foreign sperm and some- 

 times impermeable to its own sperm but quite freely permeable 

 to the sperm of other species. 



In one place Loeb tentatively suggests, "that the whole effect 

 of the alkali is simply to bring about a slight physical change in 

 the condition of the protoplasm of the egg, or the surface of the 

 spermatozoon, which facilitates the entrance of the latter into the 

 e gg " ! an d in a continuation of the same series of experiments, 2 

 published some months later, he suggests "that the main variable 

 determining the entrance of the spermatozoon into the egg may 

 be of the nature of surface tension or a function of the latter." 



In the following year Morgan 3 published a paper on "Self- 

 Fertilization Induced by Artificial Means," in which he gives an 

 account of some experiments performed on the eggs and sperm 

 of several tunicates. 



Under normal conditions the eggs of one individual cannot be 

 fertilized by its own sperm, but, by treating the eggs and sperm 

 with certain amounts of ether, he was able to get large percent- 

 ages of self-fertilizations. 



1 Loeb, University of California Publications, Physiology, Vol. I., No. 6, pp. 3Q-53- 



2 Loeb, University of California Publications, Physiology, Vol. I., No. II, pp. 

 83-85. 



3 Morgan, Journal of Experimental '/.oology, Vol. I., No. II, 1904. 



378 



