1 2 ILLUSTRATIONS 



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41. In flocks of pigeons the organization is one of 



peck-dominance rather than of peck-right 187 



42. The Dionne quintuplets also show evidence of 



a social organization among themselves 204 



43. The percentage of births that were canceled by 



deaths for the given years in Italy and Ger- 

 many 220 



44. The percentage which deaths were of births 



steadily increased during the war years 223 



45. Crepidula fornicata shows sex reversal 254 



46. Mated males of Crepidula fornicata retain that 



stage longer 256 



47. Castes of the common honey-bee 260 



48. Some ant castes 265 



49. The brown locust of South Africa has a swarm 



phase which is distinct from the solitary 

 phase 273 



