RE(^,ENERATION I05 



ena. Spencer adds that his view ' in truth is not a hypothesis,' 

 but only * a generalised expression of facts ; ' and remarks in 

 another passage, that although it is 'difficult' to imagine regene- 

 ration as a sort of process of crystallisation, '•we see that it is so.'' 

 It is just this point that I must object to. We see that it is so, 

 or rather appears to be so, s(v;ieti///es. but we also see that it is 

 often not so. If the units of the body were capable of becom- 

 ing modified at will under the influence of the whole, and of 

 crystallising into the missing part, they must be able to do so 

 in all species and in all organisms. This, however, is not the 

 case. The limb of a salamander can be regenerated, and that 

 of a lizard cannot. In a special section of this chapter I shall 

 be able to show in greater detail that regeneration depends 

 on special adaptation, and not on a general capacity of the 

 animal-body. 



It will be unnecessa.ry to give a special diagram illustrating 

 the regeneration of a single bone, such as that of the upper 

 arm, and showing the supplementary determinants of each of 

 the cells composing the bone which are necessary in order 

 that regeneration may set in at any point. The diagram given 

 for the entire limb is sufficient to make the general principle 

 clear : an approach to an explanation of the actual details is 

 out of the question, as is evident if we compare the number of 

 cells given in the diagram with that of which the bones actually 

 consist. For this reason I have not attempted to enter into 

 minute histological details, or to define the quality of the cells 

 which are capable of regeneration, — that is, to state whether 

 they belong to the periosteum or to the bone itself, and whether 

 all or only certain cells take part in the process. We only re- 

 quire a diagram which can be adapted to the actual details of 

 the processes when these are known. It is sufficient at present 

 to show that regeneration may be understood by considering 

 the activity of the cells themselves, without having recourse 

 to the assumption of an unknown directive agency. The 

 ' nisus for7nativus ' descends from its previous position as a 

 single force directing the whole, and breaks up into an un- 

 limited number of material particles which are situated in the 

 individual cells, and each of which prescribes the course of life 

 of the cell. These particles are determined as regards their 

 kind, and are distributed to their proper places so accurately, that 

 by their united effect they give rise to a composite whole, such 



