SPENCER'S PHYSIOLOGICAL UNITS 405 



by reference to the way in which pieces of a Begonia-leaf will 

 reproduce the whole plant. " The assumption to which we 

 seem driven by the ensemble of the evidence, is that sperm- 

 cells and germ-cells [better, egg-cells] are essentially nothing 

 more than vehicles, in which are contained small groups of the 

 physiological units in a fit state for obeying their proclivity 

 towards the structural arrangement of the species they belong 

 to." If the likeness of offspring to parents is thus determined, 

 it becomes manifest, a priori, that besides the transmission of 

 generic and specific peculiarities, there will be a transmission of 

 those individual peculiarities which, arising without assignable 

 causes, are classed as " spontaneous." So far, in our quotations, 

 there is no distinct suggestion of the central idea of pangenesiSj 

 nor of the transmissibility of modifications. 



But Spencer goes on to say : " That changes of structure caused 

 by changes of action must also be transmitted, hov/ever obscurely, 

 from one generation to another, appears to be a deduction from 

 first principles — or if not a specific deduction, still, a general 

 implication. . . . The units and the aggregate must act and 

 react on each other. The forces exercised by each unit on the 

 aggregate, and by the aggregate on each unit, must ever tend 

 towards a balance. If nothing prevents, the units will mould 

 the aggregate into a form in equilibrium with their pre-existing 

 polarities. If, contrariwise, the aggregate is made by incident 

 actions to take a new form, its forces must tend to re-mould 

 the units into harmony with this new form ; and to say that the 

 physiological units are in any degree so remoulded as to bring 

 their polar forces towards equilibrium with the forces of the 

 modified aggregate, is to say that when separated in the shape 

 of reproductive centres, these units will tend to build themselves 

 up into an aggregate modified in the same direction " (p. 256). 

 That is to say, representative physiological units of the body 

 congregate in vehicles which we call ova and spermatozoa, 

 carrying with them, on their journey to form a new generation. 



