364 PROTOPLASMIC ACTION AND NERVOUS ACTION 



or losing the power of development on return to sea 

 water; at about the time when the furrow begins 

 to form, there is a marked and rapid decline of extensi- 

 bihty and coherence in the plasma membrane, and the 

 eggs show rapid loss of pigment and cytolysis when 

 transferred to the dilute sea water. Eggs brought into 

 dilute sea water a few minutes after the furrow is complete 

 are found to have recovered the original resistance, and 

 swell without cytolysis. These experiments show clearly 

 that accompanying the division of the cell body there 

 is a reversible change in the properties of the plasma 

 membrane, this change involving both loss of coherence 

 and increase of permeabiHty. That the permeabihty as 

 well as the physical tenacity of the membrane is altered 

 is best shown by studying the behavior of the eggs in 

 concentrated instead of dilute sea water; during the 

 formation of the furrow the abstraction of water and 

 shrinkage are distinctly less rapid and complete than 

 before or after cleavage, a difference indicating a partial 

 loss of semi-permeabiHty at this time. Other indications 

 of increase of permeabihty during cleavage have been 

 noted by various observers (Harvey, Just, Lyon). 



According to the present theory variations of electrical 

 surface-potential should accompany these changes of 

 permeabihty; and observations made at Woods Hole 

 in 1904 by Miss Hyde,^ using fish eggs, indicate that 

 during the formation of the cleavage-furrow the blasto-j 

 disk area becomes increasingly negative relatively to the] 

 general surface of the egg. Experiments in this field 

 are, however, few in number as yet; and it would bei 

 desirable to repeat and extend these observations, using | 



* I. H. Hyde, loc. cit. 



