BIOLOGY, PSYCHOLOGY, AND SOCIOLOGY. 171 



Here, tlien, we come to a proof, more conclusive even than that 

 before given, that social actions are regarded by me as resulting 

 from mental factors. Though the specialization of functions, or 

 division of labor, is held to be analogous in living bodies and 

 social bodies though, in both cases, co-operation of the mutually- 

 dependent parts has to be effected by stimuli conveyed from one 

 to another ; yet it is shown that while in the one case this pre- 

 requisite is effected by a physical process, it is in the other case 

 effected by a psychical process. So that beyond the proofs vari- 

 ously given that the organization of each society is mainly caused 

 by the mental traits of its units, there is here given the proof that 

 these mental traits produce their results through certain mental 

 products the signs of feelings and thoughts. 



And now let me add a not unimportant conclusion brought 

 into view by this long explanation. In the course of it there has 

 become manifest to me the essential distinction, which I had not 

 before observed, between the dependencies of Sociology on Biol- 

 ogy and the dependencies of Sociology on Psychology. They con- 

 cern respectively the substance of society and the structure of 

 society. We may contemplate the social aggregate simply as a 

 mass of living units, ignoring any arrangement of its parts; or, 

 tacitly positing the existence of the mass, we may occupy our- 

 selves exclusively with the arrangement of its parts. Under the 

 one head we are concerned only with changes of quantity and 

 quality increases or decreases of the units in number, and 

 organic modifications of their natures : changes produced in the 

 course of generations by subjection of the units to certain condi- 

 tions of life. For interpreting social phenomena included in this 

 group, we depend directly upon Biology. Under the other head 

 we are concerned only with the development of this social aggre- 

 gate into an organization of mutually-dependent parts perform- 

 ing different duties the gradual evolution of structures and cor- 

 relative functions and formation of a more and more integrated 

 whole. For interpreting the phenomena included in this far 

 more conspicuous and important group, we depend directly upon 

 Psychology. Though the two can not be sharply separated, since 

 bodily life and mental life are indissolubly united, and exert 

 reciprocal influences, yet, as being respectively concerned with 

 social substance and social form, the two are sufficiently con- 

 trasted. 



The editors of the Zoological Record count 366,000 distinct species in the 

 animal world, of which 230,000 are insects and only 2,500 are mammals. 

 Next most numerous to the insects are the moUusks, 50,000 species ; crusta- 

 ceans, 20,000 ; birds, 12,500 ; fishes, 12,000 ; and arachnids, or the spider 

 family. 10.000 species. 



