CHAPTER IX. 



PHYSIOLOGICAL INTEGRATION IN ANIMALS. 



§ 305. Physiological differentiation and physiological inte- 

 gration, 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 la- 

 bour, to see that as fast as the kinds of work performed by 

 the component 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 inte- 

 gration 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 in- 

 creasing co-ordination is determined. 



Already, among the Inductions of Biolog}^, 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, 



