ORIGIN OF THE INDIVIDUAL 



257 



organization? Or, if we lean toward a mechanistic inter- 

 pretation of development or life, what kind of a 'machine' 

 is it which has such potentialities? (Fig. 133.) 



At first glance the behavior of these two classes of eggs 

 seems to afford results which are irreconcilable the former 

 A B 



Fia. 133. Diagram to show development of whole eggs and isolated cells of the 

 two cell stage. A, Dentalium; at the left, development of the whole egg; at the right, 

 development of the first two cells, when separated, into two abnormal larvae. B, Am- 

 phioxus; identical experiment at the two-cell stage resulting in two perfect small larvae. 

 (From Wilson.) 



supporting in a refined form the perennial doctrine of pre- 

 formation, and the latter its antithesis, epigenesis. But an 

 explanation is not far to seek. The difference apparently 

 depends upon the time when differentiation of the egg cyto- 

 plasm is chiefly established. If this occurs before or at 

 fertilization, so that the early divisions give rise to dissimi- 



