REGENERATION 1 23 



Finally, the complexity of the individual parts constitute tlie 

 third factor which is concerned in regulating the regenerative 

 power of the part in question ; for the more complex the struc- 

 ture is, the longer and more energetically the process of selection 

 must act in order to provide the mechanism for regeneration, 

 which consists in the equipment of a large number of ditTerent 

 kinds of cells with supplementary determinants, which are ac- 

 curately graduated, and regulated as regards their power of 

 multiplication. Thus w^e can understand, for instance, why the 

 fore-limb of a Triton becomes regenerated, while that of a bird 

 does not, although the wing is of far greater importance and is 

 much more indispensable to its owner than is the fore-limb in 

 the case of the Triton. Although there are fewer bones in a 

 bird's wing than in a Triton's limb, the former is by far the 

 more complicated structure ; for it is covered with feathers, and 

 as each quill has a special size, form, and coloration, the wing 

 must contain a large number of special determinants in its for- 

 mative cells. These determinants must all be contained and 

 arranged in the germ-plasm, so that they can be passed on 

 during embryonic development through a certain series of cells, 

 — first into the outer germinal layers, then into the epidermis 

 of the fore-limb, and finally, by the agency of further series of 

 cells arising in the course of growth, to the region to which they 

 specially belong. It is difficult enough to imagine how the 

 distribution of the determinants can possibly take place in so 

 accurate and certain a manner as must be the case in reality, so 

 that not only the shape of the feather but even every speck of 

 colour on it is accurately repeated in every individual of the 

 species ; and it might well, indeed, be considered impossible that 

 the whole of this complex mechanism should also be capable of 

 becoming modified in such a manner, that the entire wing, with 

 all its feathers and patches of colour, could be regenerated 

 from a cut surface in any part. Did this occur, the cells of any 

 section of the wing would, according to our theory, have to con- 

 tain the whole of the determinants of all the cells required for 

 the construction of the portion of the wing distal to the cut sur- 

 face as supplementary determinants, in addition to their own 

 special idioplasm ; and moreover, these determinants must then 

 be distributed proportionately among the cells of the radial and 

 ulnar, and of the upper and under surfaces of the wing, and the 

 power of multiplication of each cell and its successors would have 



