22 HEREDITY 



This obviously corresponds to the biophore of Weis- 

 mann. Such a unit would be common to all forms 

 of living matter : it would have no specific characters. 

 But if we consider the phenomena of repair — as in 

 the growth of a lizard's leg after amputation, or in 

 the development of a begonia from a leaf- fragment 

 — we note the existence of a property which, in the 

 case of repair of damaged crystals, is called polarity. 

 Thus we may use the term organic polarity, or 

 polarity of the organic units, to signify the proxi- 

 mate cause of the ability which organisms display of 

 reproducing lost parts. 



Spencer, therefore, supposed that the chemical 

 units combine into units immensely more com- 

 plex than themselves, complex as they are ; and that 

 in each organism these physiological units pro- 

 duced by this further compounding of highly 

 compound molecules have a more or less distinctive 

 or " polar " character. Obviously the phenomena of 

 repair, which led Spencer to this most important con- 

 ception, are indistinguishable in principle from any 

 other case of heredity. If, then, we desire to track 

 down to its hiding-place the ultimate material 

 structure to which all the phenomena of heredity 

 and variation must be referred, we find ourselves 

 satisfied with the 'physiological unit of Spencer, 

 re-named "gemmule," " plastidule," "determinant," 

 and I know not by how many other terms. 

 Recalling our study of the typical nucleus, we 

 remember that its chromatin is really a collection 

 of chromosomes, in which minute parts (microsomes) 

 may be detected. Where the microscope fails us, 

 theory steps in, and argues that these microsomes 



