I06 THE GERM -PLASM 



as, for instance, a series of l:)ones, together with their articular 

 capsules and ligaments, and the muscles, nerves, blood-vessels, 

 connective tissue, and integument which come into relation with 

 them. The diagram I have given to illustrate the regeneration 

 of a bone can obviously be adapted to represent any other part 

 or tissue. We must not look upon the bone as something quite 

 disconnected from the rest of the limb, as we may very likely be 

 inclined to do if we are specialists. The bone is in reality con- 

 nected most intimately along its entire surface with the surround- 

 ing tissues, — the periosteum and loose connective tissue external 

 to the latter, the numerous blood-vessels which penetrate into 

 the substance of the bone, the nerves, and so on. The first 

 rudiment of the limb consists, in fact, of a mass of mesodermic 

 cells, which give no indication of the various structures which 

 will later be developed from them. Nevertheless, their differen- 

 tiation does not, in my opinion, depend on their accidental posi- 

 tion within the limb, or in fact on any other external influences, 

 but is primarily due to their individual nature, that is. to tJie 

 constitution of tJieir idioplastn. The determinants composing 

 the id control the subsequent development of the cell and of its 

 successors. The further changes which the id undergoes in the 

 course of cell-division, and the manner in which the deter- 

 minants undergo disintegration in the ids of the daughter-cells 

 of all the subsequent generations, is decided by the composition 

 of the id. 



We can thus understand, at least to some extent, how it is 

 possible that such a complicated part as a limb, the structure of 

 which is so accurately prescribed, can arise by degrees from a 

 mass of cells which are apparently all similar to one another. 

 The harmony of the whole is primarily brought about by the 

 variation and increase of the cells, the kind and rhythm of 

 which respectively, is prescribed by the idioplasm of each in- 

 dividual cell, rather than by the mutual influence of the cells 

 durinjr their sradual differentiation. A muscle becomes de- 

 veloped at any definite spot, because one particular cell amongst 

 all the apparently similar cells in the first rudiment of the limb 

 contained the determinants which are capable of giving to a 

 large number of the successors of this cell the special character 

 of muscle-cells ; and because, again, the id of this particular 

 cell caused a rhythm of multiplication to set in, which, on 

 mechanical grounds, rendered it necessary that certain succes- 



