Experimental Studies on Germinal Localization. 67 



ticular area shows such a qualitative, as distinguished from a quan- 

 titative, pre-determination, one is led to suspect that a like con- 

 clusion may apply to other egg-regions, such as those that form 

 the gut, the prototroch, and the like ; and to conclude that however 

 detailed a prelocalization may exist in the form of regional seg- 

 regations of material, a regulative factor may always be present 

 that controls their normal combination. In this respect the un- 

 segmented egg, may, I believe, be directly compared with such 

 an adult animal as a planarian or hydroid, which, while possess- 

 ing more or less definitely specified tissues. In a typical grouping, 

 nevertheless may possess a high regulative capacity shown in the 

 process of regeneration after injury. 



The facts observed give as little clue to the nature of the regu- 

 lative factors by which the quantitative relations are determined 

 in the egg-fragment as in the fragment of a planarian or hydroid; 

 but one or two considerations deserve brief mention. It is note- 

 worthy that although the polar lobe regularly forms in the non- 

 nucleated vegetative half of a fertilized egg it is as a rule, though 

 not always, not reduced, but nearly or quite as large as in a whole 

 egg, whereas in a fertilized fragment, representing the same re- 

 gion of an unfertilized egg, the lobe is as a rule reduced to its 

 proper proportional volume. While I would not lay too much 

 stress on this without further study, it seems to indicate that the 

 power of regulation, on which the size of the lobe depends, is 

 more complete in a nucleated fragment than in an enucleated one. 

 Second, when once the polar lobe has formed, the power of regu- 

 lation seems to be lost, at least temporarily; for if a part of it 

 be cut away the second lobe is of correspondingly reduced size, 

 as is also the post-trochal region of the resulting larva. This 

 result is supported by the fact that, like the post-trochal region 

 to which it gives rise, the polar lobe in the first (virtual second) 

 division of the isolated CD half, though sometimes slightly re- 

 duced, is in general nearly or quite as large as in a whole embryo. 

 These facts prove that the size of the lobe is not determined 

 merely by the size of the piece, but by more complex conditions 

 existing apparently for only a brief period, and apparently also 

 more effective in a nucleated than in a non-nucleated protoplasmic 



