Experimental Studies on Germinal Localization. 6^ 



spheroid modified by the presence at one end of the large tro- 

 choblasts which have not like the other cells the power of con- 

 tinued multiplication, and it evidently represents a state of equilib- 

 rium towards which any segmented mass of the egg tends that 

 is devoid of the lower polar area. Whether the closure of the 

 embryos (which in the case of isolated blastomeres are at first 

 strictly partial structures) to produce this form should be con- 

 sidered as a regulation or regenerative process is largely a ques- 

 tion of definition.^ In any case the facts very clearly show that 

 the process is not perceptibly influenced by the nature of the cells 

 individually considered; nor does it, on the other hand, appear to 

 exert any appreciable effect on the nature of the individual cells 

 ("Umdifferenzierung" of Roux), as will be more clearly shown 

 in my second paper.- Certainly the closing of the embryos does 

 not lead to the least perceptible tendency towards the restoration 

 of the missing structures that are dependent on the material of 

 the lower polar area.^ I am in agreement with the opinion of 

 Fischel ('98) that, whether a regulative process or not, the 

 closing in to form a closed structure is probably explicable as a 

 result of relatively simple physical factors, though I doubt whether 

 the explanation is as simple as Fischel assumes in the case of the 

 ctenophore."* It is difficult to avoid the conclusion that these 

 same factors are operative in the establishment of the normal 

 form in a whole embryo; but to them are add in the material 

 of the lower polar area a far more complex group of factors, at 

 present not analyzable, that involve the whole process of growth 

 and metamorphosis. That a mass of cytoplasm so small should 



1 Roux ('93, p. 837) interpreted the closure of the open blastula as part of the 

 regenerative process, in opposition to Driesch ('92, p. 585), who asserted that 

 this had nothing to do with the regenerative process proper ; though he after- 

 ward took the ground that it should be considered as an initial regulative pro- 

 cess ('96, p. 88). Morgan ('01, p. 13, etc.) classes morphallaxis under the 

 head of regeneration, though not the closing in of a cut surface, which is con- 

 sidered as a preliminary process. Cf. Child, on "Mechanical Regulation" ('02). 



2 Cf. Crampton, '97, p. 55. 



3 Cf. the remark of Driesch, based especially on Crampton's experiments on 

 Ilyanassa; "1st, wie bei Gastropoden und Anneliden, echte Lokalisation der Bil- 

 dungsfaktoren im Ei anztmehmen, so schliesst das eine Regulation zum Ganzen 

 wirklich aus." ('96, p. 89.) 



■* Cf. Rhumbler, '02, Zur Strassen, '03. 



