154 ANIMAL INSTINCTS. 



in compulsion as well as aspect, to the simpler in- 

 stincts of animal existence. The life of man in its 

 every part is replete with examples of such changes ; 

 but with this general mark appended to them, that 

 they are least frequent and compulsory where the 

 mental energy is the highest. The main fact here is 

 recognised in the e#os and Averts of Aristotle ; in the 

 6 Consuetudo, deinde Natura ' of Quintilian, and in a 

 thousand maxims and common -places of our own day. 

 But physiology, as a science, defines the fact far more 

 strictly, connecting it with all the faculties, animal, 

 intellectual, and emotional, and making it the exponent 

 of many strange anomalies of individual life. When 

 we say that ' habit is a second nature,' we pithily ex- 

 press those permanent changes produced by continual 

 repetition even in the most important functions, and 

 which, thus infixed, are often transmitted from one 

 generation to another. No law, however, can yet 

 even approximately be applied to this hereditary 

 transmission. It merges in that deep mystery of gene- 

 ration in which so many of these secrets lie hidden. 



These remarks chiefly concern man, but not ex- 

 clusively so. The kindred thus denoted between in- 

 stincts and compulsory transmissible habits may be 

 seen much lower down in the scale of animal life, 

 manifestly pointing towards that ulterior question, now 

 the subject of such keen controversy, whether all 

 actions that we call instinctive may not be thus en- 

 gendered from simpler conditions of existence, granting 

 unlimited time and physical changes, unknown in 

 quantity and quality, acting from without upon animal 



