II.] ON HEREDITY. 77 



latter at the expense of the former is a demonstration that such 

 a passage actually takes place. But a closer examination 

 reveals immense difficulties. In the first place, the molecules 

 of the body devoured are never simply added to those of the 

 feeding individual without undergoing any change, but as far as 

 we know, they are really assimilated \ that is, converted into 

 the molecules of the latter. We cannot therefore gain much 

 by assuming that a number of molecules can pass from the 

 growing somatic cells into the growing reproductive cells, and 

 can be deposited unchanged in the latter, so that, at their next 

 division, the molecules are separated to become the somatic 

 cells of the following generation. How can such a process be 

 conceivable, when the colony becomes more complex, when 

 the number of somatic cells becomes so large that they sur- 

 round the reproductive cells with many layers, and when at 

 the same time by an increasing division of labour a great 

 number of different tissues and cells are produced, all of which 

 must originate de novo from a single reproductive cell ? Each 

 of these various elements must, ex hypothesis give up certain 

 molecules to the reproductive cells ; hence those which are in 

 immediate contact with the latter would obviously possess an 

 advantage over those which are more remote. If then any 

 somatic cell must send the same number of molecules to each 

 reproductive cell ^, we are compelled to suspend all known 

 physical and physiological conceptions, and must make the 

 entirely gratuitous assumption of an affinity on the part of 

 the molecules for the reproductive cells. Even if we admit the 

 existence of this affinity, its origin and means of control remain 

 perfectly unintelligible if we suppose that it has arisen from 

 differentiation of the complete colony. An unknown controlling 

 force must be added to this mysterious arrangement, in order 

 to marshal the molecules which enter the reproductive cell in 

 such a manner that their arrangement corresponds with the 

 order in which they must emerge as cells at a later period. In 

 short, we become lost in unfounded hypotheses. 



It is well known that Darwin has attempted to explain the 



^ Or is an exception perhaps afforded by the nutritive cells of the 

 &Z%^ \vhich occur in many animals ? 



^ Or more precisely, they must give up as many molecules as would 

 correspond to the number of the kind of cell in question found in the 

 mature organism. 



