CHAPTEK IX. 



PHYSIOLOGICAL INTEGRATION IN ANIMALS. 



§ 305. Physiological differentiation and physiological 

 integration, are correlatives that vary together. We have but 

 to recollect the familiar parallel between the division of labour 

 in a society and the physiological division of labour, to see 

 that as fast as the kinds of work performed by the com- 

 ponent parts of an organism become more numerous, and as 

 fast as each part becomes more restricted to its own work, so 

 fast must the parts have their actions combined in such ways 

 that no one can go on without the rest and the rest cannot 

 go on without each one. 



Here our inquiry must be, how the relationship of these 

 two processes is established — what causes the integration to 

 advance pari passu with the differentiation. Though it is 

 manifest, a priori, that the mutual dependence of functions 

 must be proportionate to the specialization of functions ; yet 

 it remains to find the mode in which the increasing co-ordi- 

 nation is determined. 



Already, among the Inductions of Biology, this relation 

 between differentiation and integration has been specified 

 and illustrated (§59). Before dealing with it deductively, 

 a few further examples, grouped so as to exhibit its several 

 aspects, will be advantageous. 



§ 306. If the lowly-organized Planaria has its body broken 

 up and its gullet detached, this will, for a while, continue 



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