REGENERATION 1 4 r 



chapter I shall have occasion to show that we must make a 

 similar assumption in the case of budding. Such assumptions 

 are indispensable if we accept the hypothesis of the germ-plasm 

 and determinants. The accessory idioplasm required for 

 budding causes the reproduction of the entire animal, and must 

 therefore contain all the determinants of the germ-plasm, and 

 must exist in the ovum before segmentation, remaining in a 

 latent condition in a definite series of cells during all the stages 

 of development. If now this accessory idioplasm were capable 

 of becoming active under certain abnormal influences, — such as 

 that produced by the destruction of the other blastomere, — a 

 regeneration of the whole embryo might thus result. 



These explanations are, however, only possible ones, and I 

 should not have been sorry to leave them out of consideration 

 altogether, for I am fully aware of their incompleteness and 

 unreliability : I merely wish to show that the observations men- 

 tioned above do not render an explanation impossible, even 

 although we are not able at present to state that any particular 

 interpretation of the phenomena is the correct one, because the 

 observations themselves are far too incomplete and deficient. 

 For this reason I shall not attempt to give a more precise 

 explanation of the peculiar development of these embryos. 



I must, however, draw attention to the different behaviour of 

 the eggs in the case of the frog and in that of Ascidians and 

 sea-urchins. Leaving aside the question of 'post-generation,' 

 we have seen that only half an embryo arises from one blasto- 

 mere of a frog's ovum, while an entire animal becomes developed 

 from one blastomere in the case of either of the other two ani- 

 mals mentioned. However imperfect the explanation I have 

 offered may be. the fundamental assumption on which it is 

 based must in general be a correct one. — viz., that the first 

 blastomeres of the ^^g of an Ascidian or sea-urchin must possess 

 a capacity which is absent in the case of the frog's ^%%- As, 

 however, forces are dependent on substances, it is probable 

 that the blastomeres of an Ascidian and of a sea-urchin contain 

 an excess of substance — the accessory idioplasm — which gives 

 them the power of regeneration, and that this substance is want- 

 ing in the blastomeres of the frog. Driesch, as already mentioned, 

 expresses a doubt as to whether the blastomere of a frog would 

 not behave in a similar manner to that of a sea-urchin, if, like 

 the latter, it could be completely separated and isolated from its 



