14 ART. 10. N. YATsn : 



Thv body ot" direct evidence recently acquired by centrifuging 

 Diethüd is growing rapidly to prove that granular localization 

 does not have so close a relation to niorphogenic factoi-s as we 

 have thonglit. And beyond all doubt it was established that visible 

 granular localization is not what we have termed irerniiunl localiza- 

 tion {(/. LiLLiE '00, CoNKLiN '09, Morgan '08 and '09). Centri- 

 fuging method has certainly brought experimental embryology into 

 a new phase. It may be remarked, however, that the new evidence 

 does not invalidate the idea of germinal localization, Ijut it carries 

 this hypothesis nearer to its original form. Taking into considera- 

 tion all the experimental evidence hitherto accumulated, we can 

 not but think that there is, independent of granular localization, 

 a definite arrangement of specified material (ground substance) 

 that is closely connected with morphogenic process (germinal 

 localization"!. But how complicated this structural arrangement is, 

 is the })oint wdiich begs further investigation. At any rate we 

 may conveniently conceive three systems superimposed one upon 

 another, viz., promorphology, germinal localization and granular 

 localization. The first two may roughly correspond to what 

 Driesch calls " Intimbau " or " Intimstruktur " and the last to 

 his "Stoft'bau." Leaving the matter of egg-organization at this 

 stage, let us consider the relation between cleavage pattern and 

 each of these systems. 



It has often been remarked that granular localization and 

 cleavage pattern stand in close relation to each other. This seems 

 true especially in such forms, in which the oöplasmic movements 

 can readily be seen (Conklin '99, '02). But the recent centrifuging 

 method has successfully proved that this relation is of secondary 

 importance in at least seven forms, viz., Arbacla, Chœtopterus, Nereis, 

 Cumingia, Hydatina, Cynthia, and Orepidula. Here, whether or 



