No. 504] THE FIXATION OF CHARACTER 721 



a " stimulus "for later development, meets with difficulties 

 in the case of plants. Here development is not due to 

 interstitial growth, as in animals, and does not involve 

 progressive differentiation of almost all the cells of the 

 body, but is brought about by the activity, at a growing 

 point, of a small group of undifferentiated, continually 

 dividing cells, from the innermost of which are laid down 

 tissues which almost immediately become fixed and un- 

 alterable in size and shape. The influence, upon such a 

 distant growing point, of structures previously laid down 

 must be slight as compared with the effect of already 

 formed structures, in animals, upon growth in which they 

 themselves are taking an active part, 



The facts of recapitulation can perhaps be understood 

 better on the principle, which we have already discussed, 

 that certain categories of characters are inherently more 

 conservative than others. It may be said that, theoret- 

 ically, even- individual tends to inherit all the peculiari- 

 ties of its ancestors ; but since life is short and history is 

 long, most of the chapters have to be omitted. It is only 

 reasonable to suppose that those features will disappear 

 first during evolutionary advance which are least con- 

 servative and least firmly fixed in the constitution of the 

 race ; and such we find to be the fact, for it is not char- 

 acters of size, shape, color and texture which are usually 

 preserved in ontogeny, but the less plastic ones of number 

 and plan. The presence of gills and their associated 

 skeletal and circulatory structures became rigidly im- 

 planted in the primitive vertebrate stock and the general 

 outline of these structures still persists in the embryos of 

 modern terrestrial forms. It is not a functional gill which 

 is repeated, however, nor one of definite shape or special 

 construction, but simply a gill cleft, with the vestiges of 

 its ancient skeleton and vascular supply. It is as though 

 what the geneticist would call the factor for the gill open- 

 ings had persisted unchanged, but that the factors for the 

 shape, size and structure of the gills had been widely 

 altered or disappeared altogether. The developing axis 



