APPENDIX V 271 



other members of the union both in their growth, nourishment, 

 and sensations. 



13. Teleological mechanism. This principle has been recently 

 clearly formulated by Pfliiger a need causes its own satisfaction, 

 e.g., the need of digestion produced by the presence of food 

 causes the secretion of the digestive fluids. 



14. Memory. Man knows by introspection that he has mem- 

 ory; we attribute it to the higher animals by common consent, 

 and there is no reason for denying its existence in the lower 

 forms. Real memory implies consciousness, otherwise it cannot 

 be known that the sensation refers to the past. 



15. Habit. This may be best denned as unconscious memory. 

 It seems to me a grave error to identify habit and real memory. 

 Habit implies that acts become easier if repeated. 



16. Consciousness. Our knowledge of this, as of memory, is 

 introspective, and is attributable to animals for the same reasons. 



17. Free will. If there be such a thing it must of course be 

 entered here. 



These are the essential categories of the phenomena of animal 

 life, and as they are all performed by colonies of cells, they must 

 be the work of the units of such colonies, or in other words each 

 one of these properties is that of a cell. There are reasons for 

 thinking that unicellular animals have the same properties. To 

 summarise, every cell performs all functions : 



1. Responds to stimuli. 



2. Maintains the vortex. 



3. Grows and divides. 



4. Inherits, varies, and bequeaths. 



Further, each cell probably has 



5. A sexual power, usually dormant. 



6. Consciousness. 



7. Memory. 



8. Habit. 



