370 E. Nezi'toii Harvey 



contraction in the muscles, bring about a loss of pigment in the 

 cells of the same organism, Arenicola larvae. McClendon-^ men- 

 tions that the parthenogenetic agents which he has used bring 

 about a loss ot pigment in sufficient concentration, and Loeb^^ 

 had already emphasized the cytolytic nature of membrane form- 

 ing substances although interpreting it in a different way. 



VI. SURFACE TENSION CHANGES IN FERTILIZED AND UNFERTI- 

 LIZED EGGS 



In the same paper-^ which was cited in discussmg the cause of 

 the movement of the pigment granules of Arbacia eggs to the 

 surface, Lillie has pointed out the relation which should exist 

 betw^een changes of permeability (accompanied b\' ionic inter- 

 change) and the surface tension of the membrane in question. 

 An increase of permeability should be accompanied b van increase 

 in surface tension (in as much as the surface tension of a film is 

 greatest when the potential difference between its two sides is 

 least). This actually does take place in Echinoderm eggs. Kggs 

 from the same females are often somewhat irregular in shape, 

 frequently being elongated, twice as long as wide. Sometimes 

 40 per cent of Arbacia eggs are in this condition and I have seen 

 practically all the mature eggs of Toxopneustes irregular just 

 after shedding. It is hard to realize that such small bodies can 

 exhibit the shapes they do especialh if t\\t\ are compared with 

 other fluid systems of the same size, as oil droplets, which main- 

 tain their spherical form through their high surface tension. If 

 such irregular eggs are fertilized with sperm or treated with 

 CH3COOH there is an immediate change. They all become 

 spherical, indicating an increase of surface tension. The round- 

 ing of eggs on fertilization takes place quite generally. Whether 

 this is actually due to a change in potential difference resulting 

 from increased permeability is not so certain but it is significant 

 that the change occurs just after the entrance of a spermatozoon 

 or after treatment with acid sea water. 



^' Science, n. s. xxx, p. 454, 1909. 



■■'^Loeb, J.: Arch. f. d. ges. Physiol, izz, p. 196, 1908. 



^'Lillie, R.: Loc. cit., p. 204. 



