ACTIVATION OF UNFERTILIZED STARFISH EGGS. 299 



artificial activation ought to yield data from which by elimina- 

 tion the essential factors common to the two processes may be 

 determined. Judging from the data available at present, the 

 most general common feature appears to be the initial increase 

 in permeability.^ It is not yet clear, however, how this change 

 can be the means of initiating the specific interaction assumed. 

 The substances which interact are assumed to be present in 

 advance in the egg; how is their interaction prevented by the 

 existence of a semipermeable surface layer? The connection 

 between change of permeability and activation is probably 

 indirect; and the analogy to stimulus and response in the 

 general stimulation-process of irritable tissues still seems the 

 best adapted to throw light on this question.^ In stimulation 

 an electrical depolarization of the plasma-membranes of the 

 irritable elements is apparently the critical event; in some way 

 this change enables the characteristic response of the irritable 

 system to take place. Similarly in the initiation of development 

 in the unfertilized egg. The agents which induce membrane- 

 formation in eggs have typically a depolarizing action on irritable 

 cells like muscle-cells — i. e., cause a negative electrical variation.^ 

 Such a change appears to result whenever surface-permeability 

 is increased ; and it seems therefore probable that this depolariza- 

 tion, as such, is what enables the union of specific substances — ■ 

 the first step in activation — to take place. We may assume 

 that one of the interacting substances is situated immediately 

 beneath the electrically polarized surface-film of the egg, that it 

 is a negative colloid, and that its tendency to unite with some 

 amboceptor-like body also present in this region is compensated 

 by the electrostatic attraction between it and the layer of 



1 Cf. my paper just referred to. In a recent paper Gray confirms McClendon in 

 finding a temporary increase in the electrical conductivity of sea-urchin eggs 

 immediately after sperm-fertilization. Cf. Gray, Journ. Mar. Biol. Ass., 1913, 

 Vol. 10, p. 50; McClendon, American Journ. Physiol., 1910, Vol. 27, p. 240. 



2 1 have discussed this analogy in more detail in the paper above cited (footnote 

 2, p. 296); also in the Journal of Experimental Zoology, 1913, Vol. 15, p. 23. 



^ For the action of cytolytic substances in producing local negative variation, 

 cf. Straub, Archiv f. exp. Path. u. Pharm., 1902, Vol. 48, p. i; Zeitschr. f. Biol., 

 1912, Vol. 58, p.|25i; 'HenzQ.-.Arch.f. d. ges. Physiol., 1902, Vol. 92, p. 451; Hermanns: 

 Zeitschr. f. Biologie, 1912, Vol. 58, p. 261; Allcock; Proc. Roy. Soc, B, 1906, Vol. 77, 

 p. 267; Journal of Physiology, 1906, Vol. 33, p. xxviii; Evans, Zeitschr. f. Biol., 1913, 

 Vol. 59, p. 397. 



