388 THE PHILOSOPHY OF BIOLOGY 



Polar bodies, 198. 



Polyzoa, 164. 



Porifera, 248. 



Potential, 61. 



Potential energy, 58, 114. 



Preformation an embryological hypothesis, 128. 



Probability, 350. 



Proteids, digestion of, 90. 



Proto-forms, 254. 



Protoplasm, nature of, 106 ; 



artificial, 106 ; disintegration of, 107 ; activities of, 107 ; similar in 



plant and animal, 294. 

 Protozoa, 247 ; 



behaviour of, 293. 

 Pterodactyls, 274. 



Races (in specific groups), 194. 



Radiation, 355 ; 



of sun, 51 ; transformation of energy of, 57. 



Radio-activity, 56, 359. 



Reality, objective, 43. 



Reception, 3 ; 



organs of, 271 ; by specialised sense-organs, 11. 



Recessiveness, Mendelian, 196. 



Reflex action, 4, 272 ; 



concatenated, 150; a complex series of actions, 6; not necessarily 

 accompanied by perception, 155; the basis of instincts, 150; a 

 schematic description, 5 ; in decapitated frog, 6 ; frictionless cerebral 

 activity, 8 ; involves a limited part of the environment, 50. 



Reflex arcs, 272. 



Regeneration, 142 ; 



in Hydra, 164 ; in sea-urchin embryo, 164 ; in Planaria, 164. 



Regression, 189. 



Reinke, and structure of protoplasm, 106. 



Reintegration in development, 171. 



Rejuvenescence, 175. 



Releasing agencies, 157. 



Reproduction, 167 ; 



asexual, 175; by brood-formation, 173; by conjugation, 173; sexual, 

 174; by division, 172; compared with minting machine, 242; of the 

 tissues, 180. 



Responses of organisms, 217 ; 



directed, 269 ; of magnet, 279 ; of green plant, 279. 



Reversibility, physical, 369. 



Rodewald, chemical nature of protoplasm, 106. 



Roux, experimental embryology, 131 ; 



development the production of a visible manifoldness, 307. 



