PHYSICS OF SEGMENTATION. I O/ 



volumes, chemical constitution, (2) nature of solvent, (3) elec- 

 trolytic dissociation, (4) heat. Changes may be brought by 

 chemical interaction, enzymes, heat, mechanical agitation, or 

 amount of solvent present. 



In the egg, which is a system of coexisting energies, it is 

 then directly with the attracting and repelling "forces," indirectly 

 with anything conditioning them, that our problem is concerned. 

 To be sure the molecules of both solvent and dissolved sub- 

 stance, the solute, must be admitted each respectively both to at- 

 tract and to repel. In the former, however, the attracting forces 

 predominate as is shown by the slight effect of temperature ; the 

 repelling may therefore be ignored. In the latter the converse 

 is the case, for the same reason. 



The form and surface of the egg at any time is accordingly de- 

 termined directly by these two energies, and indirectly by any of 

 the above enumerated conditions modifying them, for any uncom- 

 pensated potential differences which may rise through the action 

 of either internal or external causes must be equilibrated with a 

 resultant change in surface and perhaps in volume. 



The valid objection may here be offered, however, that a uni- 

 form or average decrease in surface tension does not account for 

 the change in form accompanying segmentation. This can doubt- 

 less be met by showing that, at the same time that a decrease 

 takes place, a rearrangement also results because of the exist- 

 ence in the egg of localized chemical differences, i. e., the egg 

 is organized. That these exist is shown : (i) experimentally by 

 the different staining reactions of, e. g., the nucleic and cyto- 

 plasmic cells to acid and basic dyes ; * and (2) by observed mor- 

 phological differences and changes. Granted this chemical or- 

 ganization, localized changes in it and so of the osmotic pressure 

 necessarily present in such a solution can be brought about either 

 normally by the entrance of a spermatozoon, whether its action 

 be enzymatic or chemical, or abnormally by ions, temperature, 

 agitation, or abstraction of water. Differences in osmotic pres- 

 sure thus arising may remain localized either because of mem- 

 branes within the egg, /. e., of further chemical differences, or by 

 reason of the relatively slow diffusibility of colloidal particles. 



1 Cf. the researches of Picton and Linder. 



