Experimental Studies on Germinal Localization. 251 



by virtue of the relation of the particular cytoplasmic regions to 

 the egg as a whole : the fact remains that the cytoplasmic sub- 

 stance possesses different specific qualities in different regions, and 

 that these differences persist after the regions have lost their re- 

 lation to the whole. Only by a play upon words, therefore, can 

 the conclusion be escaped that the cytoplasmic regions consist of 

 specifically different substances having a definite morphogenic 

 v^alue. The question whether these substances are to be consid- 

 ered as preformed building materials, or rather as specific deter- 

 mining materials^ (such, for example, as enzymes) is a second- 

 ary one, on which I do not propose to enter here. Holding both 

 these possibilities in view, I can see no valid objection to the frank 

 adoption, in a provisional sense, of the term "formative stuffs" 

 in the general spirit of the Bonnet-Sachs hypothesis, awaiting fu- 

 ture research, to determine what is their mode of action. We 

 must, therefore, conclude that the cleavage-pattern represents lit- 

 erally a mosaic-work of such formative stuffs that have been dis- 

 tributed by the cleavage process, and that the specification of the 

 cells is within certain limits determined by their inclusion of these 

 stuffs. If for the conceptions of qualitative and quantitative 

 nuclear divisions we substitute those of qualitative and quantitative 

 cytoplasmic divisions, a very large part of the development that 

 Roux has given to his theory in his long controversy with Driesch, 

 O. Hertwig and other writers, is, I believe, entirely valid. I 

 shall not undertake to go over the whole of this ground again, 

 but will apply these terms to a specific interpretation of certain 

 facts. 



In my preceding paper I have suggested that the difference in 

 behavior between isolated blastomeres of different forms is pri- 

 marily due to differences in the initial form and degree of segre- 

 gation. The possibility of the production of a perfect larva from 

 either half of any quarter in the egg of Amphioxus, Echinus or 

 Cerebratulus is given by the symmetrical or purely quantitative 

 distribution of materials by the first and second cleavages.' In 

 Dentalium both halves are not able to produce perfect larvae, 



'^Cf. Morgan, Regeneration, p. 89. 

 Kf. Fischel, 03, p. 7^2>- 



