X HEREDITY AND SELECTION IN SOCIOLOGY 



CHAPTER V 



Instinct 



PAGES 



Useful morphological characters due to natural selection — Correlation 

 between morphological and psychological characters — Centralisa- 

 tion of the nervous system necessary to the development of 

 consciousness — Ribot on " instinct as an inherited habit " — 

 Impossibility of accepting consciousness as the basis of instinct 

 among primitive organisms — Reflex action — Instinct a succession 

 of reflex combinations — ^Instinctive movement the result of the 

 action of external stimuli on certain cerebral centres— Correla- 

 tion of colour and instinct in Xylina — The instinct of conjugation 

 among micro-organisms — Consciousness is at the origin of com- 

 plicated series of actions adapted to a definite end — Neverthe- 

 less, instinct is not always the result of conscious volition — 

 Example of Sitaris humerales — Instinct of the sea-cucumber, 

 Cucumaria - - - 85-95 



CHAPTER VI 

 The Biological Importance of Amphimixis 

 Correlation between the age of an organic character and its persistence 

 — Amphimixis does not necessarily entail multiplication or 

 rejuvenation — Persistence of amphimixis due to the stabihty of 

 the determinants of this character — ^Natural selection causes the 

 maintenance of amphimixis — Amphimixis a necessary check on 

 excessive variation — Adaptation assured by amphimixis — Sym- 

 metrical and as3anmetrical curves — In symmetrical curves con- 

 stancy is identified with normahty — In asymmetrical curves 

 constancy is separated from normahty — Causes of asymmetrical 

 cirrves — ^No antithesis between constancy and adaptation — 

 Amphimixis ensures constancy and adaptability — Simultaneous 

 regressive variation of useless organs rendered possible by 

 amphimixis — Minute adaptation of conjugating cells to each other 

 —Summary - - ... 96-108 



CHAPTER VII 



CONSANGriNITY 



Although continual mingling of heterogeneous germ-plasms be 

 advantageous for the species, consanguinity is not necessarily 

 harmful — Biological results of exogamous and endogamous 

 pairing — Reasons of consanguineous degeneracy — Consan- 

 guineous degeneracy presupposes unfavourable variations, but 



