A DYNAMICAL HYPOTHESIS OF INHERITANCE. 49 



The doctrine that cells undergo differentiation in relation to 

 other adjacent cells, or that the destiny of a cell is a function 

 of its position (Driesch), is no doubt true. Nevertheless, we 

 have in organisms machines of such complexity, dynamical 

 potentiality, and power of transformation, that in comparison a 

 study of the theories of crystallography is simplicity itself. In 

 organisms we have the polarities of head and tail, stem and 

 root, right, left, dorsal, and ventral aspects, as definitely marked 

 out as are the relations of the axes of crystals. In the organ- 

 ism, we have diffuse, intussusceptional growth in three dimen- 

 sions, by means of the osmotic interpolation of new molecules, 

 whereas, in the crystal, growth is superficial, but consequently 

 also tri-dimensional. In the organism the molecules are mobile 

 within limits ; in the crystal they are fixed. Nevertheless, we 

 may justly regard organisms as developing after the manner of 

 crystals, but with the power of very gradually varying their 

 forms by means of variation in the structure, forms, and powers 

 of their constituent molecules, in the course of many genera- 

 tions of individuals. 



This variation may be directed by the concurrence of a 

 series of natural conditions operating dynamically (natural 

 selection). Or, interbreeding and crossing, with care or under 

 Nature, may unite by means of reciprocal integration — (fertil- 

 ization) — two molecular mechanisms whose total structure 

 and sum when thus united, as in sexual reproduction, may vary 

 by the mere combination of the two dynamical systems {egg 

 and sperm), differing slightly from one another in potentiality. 

 Finally, adaptive changes may be called forth dynamically in 

 the internal structure of such developing reciprocally integrated 

 systems that must be traced back to changes in the mechanism 

 of metabolism of the parent as well as in the germs it gives off. 

 Such changes produced in the germ must become visible in the 

 effects they produce, as transmitted formal changes exhibited 

 in the course of development. 



The tendency or trend of development, however, of a given 

 form must be pretty constant, and controlled within compara- 

 tively narrow limits by the initial adult or attained structure. 

 That is, what has been attained must formally affect that 



