190 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



soon as the requisite external conditions are present. This is 

 almost the same conception of ontogenetic development as that 

 which has been held by embryologists who have not accepted 

 the doctrine of evolution : for we have only to transfer the 

 primary cause of development, from an unknown source within 

 the organism, into the nuclear substance, in order to make the 

 views identical. 



It appears at first sight that the knowledge which has been 

 gained by studying the indirect division of nuclei is opposed to 

 such a view, for we know that each mother-loop of the so-called 

 nuclear plate divides longitudinally into two exactly equal 

 halves, which can be stained and thus rendered visible. 



In this way each resulting daughter-nucleus receives an equal 

 supply of halves, and it therefore appears that the two nuclei 

 must be completely identical. This at least is Strasburger's 

 conclusion, and he regards such identity as a fundamental fact, 

 which cannot be shaken, and with which all attempts at further 

 explanation must be brought into accord. 



How then can the gradual transformation of the nuclear sub- 

 stance be brought about ? For such a transformation must 

 necessarily take place if the nuclear substance is really the 

 determining factor in development. Strasburgcr attempts to 

 support his hypothesis by assuming that the inequality of the 

 daughter-nuclei arises from unequal nutrition ; and he therefore 

 considers that the inequality is brought about after the division 

 of the nucleus and of the cell. Strasburger has shown, in a 

 manner which is above all criticism, that the nucleus derives 

 its nutrition from the cell-bod}^ but then the cell-bodies of the 

 two ex hypothcsi identical daughter-nuclei must be diftcrent 

 from the first, if they are to influence their nuclei in difterent 

 ways. But if the nucleus determines the nature of the cell, it 

 follows that two identical daughter-nuclei which have arisen by 

 division within one mother-cell cannot come to possess unequal 

 cell-bodies. As a matter of fact, however, the cell-bodies of 

 two daughter-cells often differ in size, in appearance, and in 

 their subsequent history, and these facts are sufficient to prove 

 that in such cases the division of tlic nucleus must have been 

 unequal. It appears to me to be a necessary conclusion that, in 

 such an instance, the mother-nucleus must have been capable 

 of splitting into nuclear substances of differing qualit}'. 1 think 



