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as affect these characters, are limited and co-ordinated in relation to 
the physiological necessities of somatic equilibrium. Variation must 
therefore, in this respect, be regarded as a function not of the germ¬ 
cell, but of the whole organism. 
The above argument refers primarily to determinate specific 
variations and is admittedly not so cogent in the case of sporadic 
individual mutations; for if the latter were small and fortuitous 
there may be sufficient latitude for readjustment during ontogeny, 
and the unfavourable combinations would be eliminated by individual 
extinction. But fortuitous variations, whether continuous or dis¬ 
continuous, will not account for the evolution of complex functional 
mechanisms which involve the co-ordinated interaction of several 
different structural characters without the arbitrary postulation of 
various correlations that virtually deprive them of their fortuitous 
character. As we shall subsequently see, such sporadic mutations 
unquestionably do occur, but they are not very important factors 
in evolution. 
IV. If, therefore, germinal variations are in some way somatically 
conditioned, it should be possible to learn something of the nature 
of this conditioning process. The Lamarckian theory of functional 
inheritance is an attempt in this direction, but its application is 
obviously restricted to heritable characters for which it is possible 
to assume an antecedent somatic origin. We shall endeavour to 
show however, that there is a more general relation between the 
somatic and germinal cycles, of which alleged instances of functional 
inheritance are only special cases. 
It has been previously noted that different hereditary types are 
not all equally efficient from the physiological point of view. Let 
us proceed therefore to examine if germinal variations are in any 
way correlated with physiological efficiency. Now efficiency can be 
defined most exactly in terms of energy. The organism is continuously 
or periodically assimilating energy from the primary environment. 
Some of this energy may be conserved for a while in the secondary 
environment, e.g. as the internal reserve food material of plants, as 
the energy of the nervous system available for complex psychical 
activities, or as the external food stores accumulated by the instinctive 
and intelligent behaviour of the higher animals. Eventually, however, 
it is all dissipated in the various environmental reactions associated 
with the different organic activities. The relative efficiency of 
different types is the ratio of the energy assimilated to that expended 
in the process of assimilation. This definition is applicable to all 
