VIIL] 



HOMOLOGIES. 



187 



sible, to see lioiu external conditions can have produced, 

 or even have tended to produce them. For example, we 

 may take the migration of an eye of the sole from one side 

 of the head to the other. What is there here either in 

 the darkness, or the friction, or in any other conceivable 

 external cause, to have produced the first beginning of 

 such an unprecedented displacement of the eye ? Mr. 

 Spencer has beautifully illustrated that correlation which 

 all must admit to exist between the forms of organisms 

 and their surrounding external conditions, but by no means 

 proved that the latter are the ccnose of the former. 



PLEUROIiECTIDJE, WITH THE PECtJLIARLT PLACED ETE IN DIFFERENT POSITIONS. 



Some internal conditions (or in ordinary language some 

 internal power and force) must be conceded to living 

 organisms, otherwise incident forces must act upon them 

 and upon non-living aggregations of matter in the same 

 way and with similar effects. 



If the mere presence of these incident forces produces 

 so ready a response in animals and plants, it must be that 

 there are, in their case, conditions disposing and enabling 

 them so to respond, according to the old maxim, Quicq-aid 



