MECHANISM OF MEMBRANE FORMATION 217 
Bataillon has expressed a similar view, but both authors 
have apparently overlooked the writer’s former statements. 
I have recently omitted to emphasize this idea of a secretion 
since it is merely hypothetical and moreover the word “‘secre- 
tion” is not clear from a physicochemical viewpoint. I 
therefore preferred the expression ‘‘cytolysis of the cortical 
layer of the egg,’’ which is a clearer expression of what actually 
occurs and which is better understood from a physicochemical 
viewpoint. It may be that the action of cytolytic agents upon 
the egg merely induces secretion, or that secretion is in all cases 
in the ultimate analysis a form of cytolysis. 
Since, however, the rise of the rate of oxidations is the essen- 
tial feature in the causation of development in the egg of the 
sea-urchin; and since this rise is also brought about by com- 
plete cytolysis of the egg, it seems safer to say that the 
cytolysis of the cortical layer of the egg (which results in 
membrane formation) is the essential feature in the causation 
of development. 
10. Harvey has expressed the view that the essential con- 
dition for the formation of the membrane is an increased per- 
meability of the egg surface for a membrane substance which 
passes out and hardens to a membrane in contact with sea- 
water.! Ries? and Elder*® assume that this hardening occurs 
in contact with the chorion which surrounds the egg. It is 
possible that the droplets, which initiate the membrane forma- 
tion quite frequently in the egg of S. purpuratus, are really a 
secretion of a colloid which upon coming in contact with sea- 
water swells by absorbing sea-water and which hardens at 
its outer surface to the characteristic membrane. Still, one 
wonders why this should be called a secretion, since complete 
cytolysis of the egg by saponin also results in membrane 
formation. 
1 Harvey, Jour. Exper. Zool., VIII, 355, 1910. 
2 Ries, Centralbl. f. Physiol., XXIII, 369, 1909. 
3 Elder, Archiv f. Entwicklungsmechanik, XXXV, 145, 1912. 
