52 THE FIRST PRINCIPLES OF HEREDITY 



body could, according to him, neither be inorganic chemical 

 molecules, as not having the properties of life, nor, on the 

 other hand, morphological, i.e., cellular, because the cells 

 themselves are already organized ; but these units could 

 only lie between both, and were therefore called by Spencer 

 " physiological " or " constitutional " units. Further, just 

 as a crystal in a suitable medium will complete itself and 

 crystallize in its proper form, so the physiological units 

 possess " organic polarity " — that is, they have, as already 

 mentioned, the power of arranging themselves into the 

 shape of the body to which they belong. The units are 

 different for each species, and also vary slightly according 

 to the peculiarities of each individual, but all the units of 

 each body are alike (in this respect Spencer's theory differs 

 fundamentally from the three others to be discussed), and 

 the formation of the different tissues, organs, etc., is solely 

 due to the different arrangement of the units according 

 to the influence and local condition of neighbouring units. 

 \i*' The germ-cells are," to quote Spencer's own words, 

 " 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. . . . There is no 

 warrant for the assumption that they possess powers 

 fundamentally unlike those of other cells. The inference 

 to which the facts point is that they differ from the rest 

 mainly in not having undergone functional adaptations." 

 Spencer imagined, we see, the germ-cells as an assembly 

 of physiological units derived from the body, and ready 

 to start the new individual under appropriate conditions. 

 He further maintained, and tried to prove from " first 

 principles," that any force acting on the totality of the 

 body, and modifying its units, must necessarily react on 

 and remould all the units of the body in harmony with this 

 new influence, not excepting those physiological units which, 

 " when separated from the body in the shape of repro- 

 ductive centres/' build themselves up into the new indi- 



