Physiological and Psychological Heredity. 279 



are transmitted to the second generation, and preserved there, 

 which are developed only in the third. 



Darwin also explains how modifications of bodily or mental 

 habits may be hereditary. ' According to our view, we need only 

 suppose that certain cells come to be modified, as well in their 

 structure as in their functions, and then they give out gemmules 

 similarly modified . . . When a psychic attribute, a mental habit, 

 or insanity is hereditary, we must hold that there has really taken 

 place a transmission of some effective modification, and this, on 

 our hypothesis, would imply that gemmules springing from modified 

 nerve-cells are transmitted to the descendants.' Of course these 

 modified habits become fixed only in time, since the organism 

 must subsist amid novel conditions for a considerable period, so 

 that these may act upon it, modify its cells, and make possible the 

 transmission of a larger and larger number of modified cells. 



In the preceding remarks we have reasoned only from physio- 

 logical data. But we know that in the question of heredity the 

 antithesis of psychological and physiological is a simple difference 

 of standpoint. These cells and gemmules are not brute, inani- 

 mate matter ; they are possessed of force, of life, of tendencies, and 

 we have seen that it is as difficult to conceive of the material 

 without the spiritual as of the spiritual without the material. There- 

 fore the hypothesis is applicable as well to mental as to organic 

 heredity, and if it holds good for the one, it holds good also for 

 the other. It may, in fact, be seen how well the two orders appear 

 to correspond. 



In the physiological order, at its lowest stage, we have as an 

 irreducible element the cell, or physiological unit, possessed of a 

 life of its own. From the consensus of countless lives of this kind 

 results the general life of the being whose unity appears to us as 

 a resultant, a harmony. This harmony, in proportion as we ascend 

 the scale of organisms, tends more and more to perfect unity, with- 

 out ever reaching that ideal. 



In the psychological order, at its lowest stage, we have as the 

 irreducible element or psychological unit, force as it exists in every 

 cell, or, at least, nerve-power as it exists in every nerve-cell. From 

 the consensus of all these infinitesimal psychical acts, centralized 

 in the ganglia, and afterwards in the brain, results psychological 

 13 



