PHYSICS OF SEGMENTATION. Ill 



I . Chemical Changes in Colloidal Particles by (a) Chemical Methods. 



Other conditions such as the amount of solvent being assumed 

 as constant, the first class of changes can in theory be caused by 

 any agent which increases the number of molecules or of parti- 

 cles, i. c., which causes a splitting up of these within the egg. 

 For, as is well known, in a given volume the pressure varies 

 directly with the number of molecules. Under these circum- 

 stances, in order that subsequently there may be equilibrium 

 between pressure and tension, both potentials must decrease, the 

 latter however presenting a relative rise ; at the same time both 

 the volume and surface increase, water is absorbed, and the 

 medium outside the cell is really of smaller volume and greater 

 pressure than before. 



This series of events agrees with that which we have seen must 

 take place in segmentation, viz., an average decrease of tension. 

 Confirmatory of the correctness of our theory and quite agreeing 

 with it are a number of experimental methods for obtaining arti- 

 ficial parthenogenesis when the direct effect can be only chemical 

 or ionic or both, but in any case not purely electronic. Thus in 

 Asterias eggs HC1 is effective, but not KC1, from which a specific 

 H ion effect is inferred. * So also are Ca ions alone effective for 

 Amphitritus? 1 (The effect of the hydroxyl ion, or of O, can 

 have only the same direct chemical effect primarily ; by these 

 conditions segmentation is retarded or exhibited, thus indicating 

 that for segmentation analytic processes are essential ; for, e. g., 

 oxygen in the presence of ferments means a splitting up of mole- 

 cules.) The accepting of a specific chemical effect of these ions is 

 not invalidated by the admission of an " electronic" effect also, 

 but is necessitated by just such data as the above, which are the 

 results of an application of the " method of difference." Just 

 how this chemical effect is caused, whether directly by action on 

 the protoplasm, or indirectly by first making certain " prefer- 

 ments " in the egg active cannot be definitely stated, but this 

 deficiency does not in itself alter the correctness of the above 

 view. The effectiveness of another practical method is thus found 



1 Loeb, Fischer and Neilson, Archiv fur geschichtliche Physiologic, Bd. 87, 1901 ; 

 previously cited. 



2 Fischer, loc. cit. 



