150 



INDEX 



Nasal organ, 27. 



Natural selection, 93-110. 



Nerve fibre, 14. 



Nerves, 13-16. 



Nervous system, 13-26. 



Nest building, 22-24, 25. 



Night hawk, 106. 



Northern hemisphere, fluctuations 



in numbers of animals, 60-64. 



, land masses, 51, 52. 



, winter conditions, 53- 



64. 

 and seed-eating birds, 



62, 63. 

 Nostril, 28. 



Oidemia deglandi, 7. 

 Olfactory lobe, 18. 

 Ova, 41. 



Ovariectomy, 43. 

 Ovary, 38, 39, 41. 

 Owls, 36, 62. 



Palinurus, 30. 

 Pallas' sandgrouse, 108. 

 Pancreas, 38. 

 Para-thyroid, 38. 

 Parrots, 8, 29. 

 Partridge, 96. 

 Pecten, 35. 

 Peewit, 108. 

 Pelican, 28. 

 Penguin, 79. 

 Perdix perdix, 96. 

 Perilymph, 32. 



Pia mater, 19. 

 Pigeon, 24, 81. 

 Pineal, 38. 

 Pituitary, 38. 

 Pleistocene; 68. 



glaciations, 69, 70, 71, 72. 



Pliocene, 96, 100, 109. 

 Pons varolii, 21. 

 Posterior colliculus, ZZ. 

 Preen-gland and nutrition, 58. 

 Pyramids, 21. 



Raven, 136. 



Reflex arc, 14, 15, 16. 



Reproductive organs, see gonads. 



Rhythm, 126, 127. 



Reptiles, 6, 7, 9, 13, 21, 35, 36, 



103. 

 Respiration, 11, 12. 

 Retina, 34, 35. 

 Rods (of retina), 34, 35. 



Salmon, 47. 



Scoter, white-winged, 7. 



Sea-Uon, 47, 79. 



Sea-snake, 47. 



Seal, 47. 



Seed-eating birds, 63. 



Semi-circular canals, 32, 3>3>. 



Seminiferous tubules, 40. 



Sense organs, 13, 26-36. 



Sex-reversal, 43. 



Sialia currucoides, 131. 



Sight, 35. 



Skull, 26, 27. 



Smell, 27, 28. 



