34 ART. 17. — N. YATSÜ. 



15. In Ca-free sea-water clifrerentiation and embryogeny is 

 inhibited ; nevertheless the blastoraeres increase in number. 

 When such cell-masses are put into ordinary sea-water, they 

 recover their differentiating power. 



16. On isolated cells produced by Ca-free sea- water, a very 

 few cilia may be formed scattered irregularly on the surface of 

 the cell, while in normal position these cells acquire cilia only 

 in a restricted area. 



IV. Conclusion. 



In this paper two important lines of study in attacking the 

 problem of egg-organization have been left entirely untouched, 

 viz., cytogeny and experiments by means of centrifugal force. 

 There can be no doubt that these, especially the latter, if proper- 

 ly applied, would be a great help in understanding the nature 

 of the nemertine egg. Yet so far as they went, my experiments 

 yielded results of no less importance beyond those noted in pre- 

 vious papers. Two points at least are, I think, worth considering. 



The one is that by germinal prelocalization (of the ground 

 substance) we should understand qualitative localization and not 

 quantitative, as maintained by Wilson in the case of the polar 

 lobe of the Benialium egg (Wilson '04 a pp. 42, 43, Q>Q>). In 

 other words organ bases have no hard and fast line of boundary 

 between them, though they may in some cases look as if they 

 had, owing to granular localization. Driesch's conception of 

 " auimality " and " vegetability " (Driesch '02) comes the nearest 

 to expressing tlie real nature of germinal localization. Yet it 

 seems to me that the egg has something more precise in addition 

 to mere " animality " and " vegetability," that is, something for 



