Experimental Studies on Germinal Localization. 255 



able with such a view, and he has steadily maintained the position 

 that the development of every animal presents a combination of 

 self-differentiation and correlative or dependent differentiation, 

 the relation between which varies more or less widely in different 

 cases/ Only the most thorough experimental study can deter- 

 mine what this relation is in any individual case. The hypothesis 

 of qualitative nuclear division is no doubt responsible for the dis- 

 favor with which the conception of self-differentiation was re- 

 ceived by many writers, who either relegated it to a position of 

 quite minor importance or rejected it in toto, adopting only hy- 

 potheses of correlative differentiation, or advocating a less clearJv 

 defined conception of the "organism as a whole," to which the 

 differentiation of the cells was assumed to be subject. O. Hert- 

 wig's theory of cellular interaction is a clearly formulated conr 

 ception of this type, cleavage being assumed to be merely a multi- 

 plicative process, producing qualitatively equivalent blastomeres 

 that differentiate by cellular interaction {e. g., '92, p. 481, '93, p. 

 793). "Die Zellen determiniren sich zu ihrer spateren F^igenart 

 nicht selbst, sondern werden nach Gesetzen, die sich aus dem Zu- 

 sammenwirken aller Zellen auf den jeweiligen Entwicklungsstu- 

 fen des Gesammtorganismus ergehen, determinirt" ('98, p. 144). 

 Cell-lineage, therefore, has only an incidental significance, arising 

 from the continuity of development, which involves the deriva- 

 tion of each part from an earlier group of cells, itself in turn the 

 product of a still earlier one ('92, p. 479). Whitman ('93), in 

 his singularly thoughtful and suggestive essay on the "Inadequacy 

 of the Cell Theory of Development," while repudiating the 

 theory of cellular interaction as such, urged with great force the 

 subordination of the Individual cells in development to the or- 

 ganization of the embryo as a whole — a conception which, though 

 differing widely in its form of expression, has, I think, much in 

 common with Driesch's theory. The same general view is very 

 specifically interpreted in Child's valuable descriptive paper on 

 the cell-lineage of Arenicola ('00), in such statements as the fol- 



^C/^. Roux, '88, p. 455, and elsewhere. Heider, in his suggestive survey 

 of the determination-problem ("00), and Fischel, in his more recent discussion 

 (03), takes the same ground. See also Korschelt and Heider, '02. 



