ACQUIRED VARIATIONS 145 



pendently. Thus we can see that a modifying force acting 

 on the Amphioxus fertilised ovum, or the first two or four 

 division-results, really acts on a " primitive type," whereas 

 at a later stage of development it acts on already differen- 

 tiating types ; and we should naturally suppose that if an 

 acquired variation were to be exactly " reproduced " in the 

 offspring, the modifying force would have to commence its 

 action on the " primitive type " cell. 



If this were to be called X, with the power of becoming 

 somatic tissues, S, and also X once more, then it is clear 

 that a force commencing its action on the first mentioned 

 X could, by continued action during development, cause the 

 appearance of modified somatic tissues, Sm, and of modi- 

 fied sexual elements, Xm. The fertilisation of one Xm 

 by another would, other things being equal, result in an 

 offspring with somatic tissues modified as Sm. 



On the other hand, we might suppose that if the modifying 

 force commenced its action on already differentiating early 

 cells, the actual tissue variations produced could not be 

 faithfully " reproduced " in the offspring. For if the 

 parental variations were Sn, and Xn, their evolution would 

 have to start from the beginning of the offspring's cycle, 

 and not from the point at which in the parental cycle the 

 modifying force commenced its action. The offspring's 

 variation might be So, and Xo. 



In a word, we suppose that important as the early 

 application of modifying force is for the acquisition of 

 variation, it is an even more important condition for the 

 reappearance of the variation in the offspring. 



It would appear, however, that, at times, for the suc- 

 cessful reappearance of an acquired variation the modifying 

 force must also continue its action till the organism produces 

 its sexual elements, or right on to the end of the growth- 

 cycle. At least this was proved to be so in experiments 

 with the transmission of colour modification in the Colorado 

 Beetle, as mentioned in Prince KropotMn's paper. 



The main points to which we return are : — 



That the Acquired Variation is the result of Environ- 

 mental action. 



That Environment produces its results by action on the 



10 



