PHYSIOLOGICAL INTEGRATION IN ANIMALS. 383 



those same actions by which bones, muscles, and ligaments 

 are specialized. But adequate treatment of this division of 

 the subject is at present scarcely possible. 



What little of fact and inference has been above set down, 

 will, however, serve to make comprehensible the general truths 

 respecting which, in their main outlines, there can be no 

 question. Beginning with the feebly-differentiated sponge, 

 of which the integration is also so feeble that cutting off a 

 piece interferes in no appreciable degree with the activity 

 and growth of the rest, it is undeniable that the advance is 

 through stages in which the multiplication of unlike parts 

 having unlike actions, is accompanied by an increasing inter- 

 dependence of the parts and their actions; until we come to 

 structures like our own, in which a slight change initiated in 

 one part will instantly and powerfully affect all other parts — 

 will convulse an immense number of muscles, send a wave of 

 contraction through all the blood-vessels, awaken a crowd of 

 ideas with an accompanying gush of emotions, affect the 

 action of the lungs, of the stomach, and of all the secreting 

 organs. And while it is a manifest necessity that along with 

 this subdivision of functions which the higher organisms show 

 us, there must be this close co-ordination of them, the fore- 

 going paragraphs suggest how this necessary correlation is 

 brought about. For a great part of the physiological union 

 that accompanies the physiological specialization, there ap- 

 pears to be a sufficient cause in the process of direct equili- 

 bration; and indirect equilibration may be fairly presumed a 

 sufficient cause for that which remains. 



