March 2, 1906.] 



SCIENCE. 



343 



exist, the protoplasm from between the yolk 

 spherules gathers about the spermatozoon. 

 There is, moreover, no certainty that the same 

 protoplasm remains continuously in a given 

 region. The regions persist, but in view of 

 the observations on ectosarcal activities in 

 eggs and the extensive Sowings of cytoplasm 

 to which Conklin himself has devoted so 

 much attention, it seems very probable that 

 there is extensive physical interchange of pro- 

 toplasm between various parts of the egg. For 

 example: is there any certainty that the area 

 of clear protoplasm escaping from the nucleus 

 at maturation and later giving rise to ecto- 

 derm really consists throughout of the same 

 protoplasm? There is no visible boundary be- 

 tween it and other portions of the cytoplasm. 

 In short, how can we identify the actual 

 formative substances, if such exist, and how 

 can we be certain that they do exist ? Caution 

 is certainly necessary along this line; observa- 

 tion alone does not afford a sufficient basis. 



The final section of the paper is devoted to 

 a general discussion of the problem of egg 

 organization and its genesis. The first part 

 of the section is largely a resume of our 

 knowledge and opinions regarding polarity, 

 symmetry and localization and only certain 

 points need be considered. 



In the opening sentences of the section the 

 following statement occurs: 



For our present purposes tlie organization of 

 the germ cells * * ♦ may be held to include 

 phenomena of polarity, symmetry and localiza- 

 tion; it obviously includes other things also, such 

 as regeneration and regulation, which are not, 

 however, objects of investigation in this work. 



In the discussion of localization the position 

 is taken that experiments with egg fragments 

 are no test of the presence or absence of dif- 

 ferentiation and the ascidian egg is cited as 

 a case in point; here the cleavage is deter- 

 minate, the differentiations of the various 

 parts of the unsegmented egg are very great, 

 yet experiments have apparently demonstrated 

 the totipotence of the first four blastomeres. 

 From consideration of these facts Conklin is 

 led to the following conclusion: 



Just as some adult forms show little capacity 

 for regeneration or regulation while others of 



equally complex differentiation show this power 

 in high degree, so it seems that the capacity for 

 regulation shown by eggs is more or less inde- 

 pendent of their differentiation. 



Incidentally it would be interesting to know 

 on what facts the first half of this statement — 

 that regarding adults — is based. To the writer 

 there seems to be no escape from the conclu- 

 sion that an isolated blastomere capable of 

 producing a whole embryo is in some way 

 more like the whole egg than another without 

 such power. Moreover, it was admitted in 

 the sentence quoted a few lines above that 

 egg organization must include the phenomena 

 of regulation. Even if we follow Conklin and 

 adopt Roux's view of two different methods 

 of development, direct and indirect, the or- 

 ganization must provide for each. There is 

 something very like a dilemma here. 



This is an excellent example of the difficul- 

 ties involved in maintaining the position that 

 the visible cytoplasmic differentiations are 

 foi-mative in character. How far that is the 

 case observation alone can never determine. 

 Conklin says ' all the experiments in the 

 world could not have shown as satisfactorily 

 as direct observation has done the remarkable 

 cytoplasmic differentiations and localizations 

 of this egg ' — viz., the ascidian. But it is 

 equally true that all the observation in the 

 world could not have shown as satisfactorily 

 as experiment has done — and we may add, 

 will do — how far these cytoplasmic differen- 

 tiations and localizations are from represent- 

 ing the actual formative powers of the egg. 



As regards the genesis of egg organization, 

 Conklin believes that the differentiations of 

 eggs, blastomeres and possibly other cells also 

 are the result of two processes, the genesis of 

 unlike substances and their localization. The 

 escape of nuclear material into the cell body, 

 and the formation there of specific substances 

 and their localization are regarded as afford- 

 ing a specific mechanism for nuclear control 

 of development ' and as harmonizing the facts 

 of cytoplasmic organization with the nuclear 

 inheritance theory.' As a case in point, the 

 distribution of the sphere material from the 

 last oogonic division is cited. Conklin holds 

 that a part of this material forms the yolk 



