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premature comparisons between social organizations 

 and animal or vegetable organisms. 



The existence of such exaggerations, which have 

 caused a reaction such as recently induced an emi- 

 nent American economist to declare the bankruptcy 

 of biological sociology, is perhaps due to the fact 

 that, with a few distinguished exceptions, bio- 

 sociological investigations have hitherto been con- 

 ducted either by naturalists with a limited know- 

 ledge of social questions, or by sociologists whose 

 training in biology was incomplete and superficial. 



To prevent this danger, our researches in the 

 same subject have been made separately from the 

 social side, and from the biological side, and have 

 now been co-ordinated and combined. 



This work was commenced in May 1893, with 

 the collaboration of our friend M. Dollo, the curator 

 of the Natural History Museum at Brussels. In 

 June 1894, however, M. Dollo's many occupations 

 no longer permitted of his collaboration. The zoo- 

 logical part was therefore completed by M. Jean 

 Demoor, to whom most of the facts quoted in the 

 first book were given by M. Dollo, whose assistance 

 we most gratefully acknowledge. 



