202 CONTINUITY OF THE GERM- PLASM AS THE [IV. 



re-transformation to become the rule. It is also obvious that 

 the complex structure of the germ-plasm which potentially 

 contains, with the likeness of a faithful portrait, the whole 

 individualit}' of the parent, cannot be represented by only ten 

 characters, but that there must be an immensely greater num- 

 ber; it is also obvious that the possibilities of the arrangement 

 of single characters must be assumed to be much larger than 



two; so that we get the formula (-) , where /> represents the 



possibilities, and ;/ the characters. Thus if n and p are but 

 slightly larger than we assumed above, the probabilities be- 

 come so slight as to altogether exclude the hypothesis of a 

 re-transformation of somatic idioplasm into germ-plasm. 



It maj' be objected that such re-transformation is much more 

 probable in the case of those germ-cells which separate early 

 from the somatic cells. Nothing can in fact be urged against 

 the possibility that the idioplasm of (e. g.) the third generation 

 of cells may pass back into the condition of the idioplasm of the 

 germ-cell; although of course the mere possibility docs not 

 prove the fact. But there are not many cases in which the 

 sexual cells are separated so early as the third generation : and 

 it is very rare for them to separate at any time during the true 

 segmentation of the QZ%. In Daphnidac (^Moina) separation 

 occurs in the fifth stage of segmentation ^, and although this is 

 unusuall}' early it does not happen until tlie idioplasm has 

 changed its molecular structure six times. In Sagitta- the 

 separation does not take place until the archentcron is being 

 formed, and this is after several hundred embryonic cells have 

 been produced, and thus after the germ-plasm has changed its 

 molecular structure ten or more times. But in most cases, 

 separation takes place at a much later stage ; thus in lij'droids 

 it does not happen until after hundreds or thousands of cell- 

 generations hav^e been passed through ; and the same fact 

 holds in the higher plants, where the production of germ-cells 

 frequently occurs at the end of ontogeny. In such cases the 

 probability of a re-transformation of somatic idioplasm into 

 germ-plasm becomes infinitely small. 



It is true that these considerations onl}' refer to a rapid and 



' Grobben, ' Arbciten d. Wicn. Zool. Instituts,' Bd. II. p. 203. 

 ' Butschli, ' Zeitschriit f. wiss. Zoo!.' Bd. XXIII. p. 409. 



