156 J. F. MCCLEXDOX. 



it is fertilized or made parthcnogenetic with acetic acid, indicating 

 increased permeability to ions. 



Lyon and Shackell 1 and Harvey 2 observed that methylene 

 blue and neutral red enter fertilized eggs more quickly than 

 unfertilized eggs. Harvey supposed that only the free color 

 base (undissociated) entered, since the addition of a little acid 

 to the sea water prevented the staining of the eggs. 



Mathews 3 considered the penetration of stains into the egg 

 as a chemical process (the stain forming a salt combination with 

 the lecithin or proteins of the egg surface). 



Harvey observed, further, that NaOH penetrates fertilized 

 more easily than unfertilized eggs, but the eggs are killed by the 

 alkali. 



The fact that the unfertilized frog's egg continues to swell for 

 a long time in water (Biataszewitz) whereas the osmotic pressure 

 of the fertilized frog's egg is quickly reduced to equal that of the 

 medium (Backmann and Runnstrom) indicates increase in perme- 

 ability to osmotic substances on fertilization. In this connection 

 it is interesting to note that Bataillon, 4 Brachet, and myself 5 

 caused the unfertilized frog's egg to rotate normally and segment 

 merely by pricking it. 



1 1 has been supposed by various observers that the "forma- 

 tion" of the fertilization membrane in very closely related to the 

 segmentation of the egg. Loeb observed that the sea urchin's 

 egg may develop without the formation of a fertilization mem- 

 brane, and I have confirmed this observation, and shown that 

 it is very probably wrong to suppose that this is a case of failure 

 in "pushing out" of the membrane. Apparently "membrane 

 formation" is not essential for the segmentation of the egg, 

 although by furnishing protection it may insure the development 

 of the embryo. 



Loeb postulated that an osmotically active colloid exists in 

 the unfertilized egg, but is so covered with lipoids that it does 

 not absorb water until it is squeezed out or otherwise exposed 



1 Science, 1910, XXXII., 250. 

 = Ibid., p. 565. 



3 Jour. Phurmacol. and Exp. Ther., 1910, II., 201. 



4 Arch. Zoo/. Exper., 1910 (5), VI., 101. 



8 McClcntlon, Amer. Jour. Physiol,, 1912, XXIX.. 298. 



