The Physiological Unit. 175 



the development of any organism, a combination of 

 internal forces that expend themselves in working 

 out a structure in equilibrium with the forces to which 

 ancestral organisms were exposed." * The form of 

 each species of organism is determind by a peculiarity 

 in the constitution of its units. That is, the per- 

 manent characteristics of every organism are deter- 

 mind by the physiological, units, while the forces in 

 the environment tend to produce modifications of the 

 structure. 



In criticising the theories of Dr. Erasmus Darwin, 

 Lam ark, and Professor Owen, Mr. Spencer condemns 

 the ascription of organic evolution to " some aptitude 

 naturally possessed by organisms." "In brief," he 

 says, " this assumption of a persistent formative power 

 inherent in organisms and making them unfold into 

 higher forms is an assumption no more tenable than 

 the assumption of special creations ; of which, indeed, 

 it is but a modification ; differing only by the fusion 

 of separate unknown processes unto a continuous un- 

 known process." ( Yet Mr. Spencer cannot avoid the 

 use of similar terms. When he is most emphatic in 

 repudiating all discipleship in any school which 

 acknowledges the operation of supra - dynamical 

 powers, his " speech bewrayeth " him. He speaks of 

 proclivities, tendencies, power of arranging themselves, 

 as characteristic of his units. Of these attributes, 



* Biology, Vol., II. If 8. t Ibid., Vol. L, 144. 



