262 SYMBIOGENESIS 



so far as wholly to destroy the primary physiological com- 

 munity of labour. 



Neither could it very well be carried so far except in 

 abnormal (parasitic) cases, where self-gratification rather than 

 bio-economic contribution is becoming the order of the day and 

 permanence is sacrificed. 



As in societies the adaptation of special classes to special 

 duties does not entirely disable these classes from performing 

 each others' duties on an emergency ; so in organisms, tissues 

 and structures that have become fitted to the particular offices 

 they have ordinarily to discharge, often remain partially able 

 to discharge other offices. It has been pointed out by Dr. 

 Carpenter, Spencer tells us, that "in cases where the different 

 functions are highly specialised, the general structure retains, 

 more or less, the primitive community of function which 

 originally characterised it." 



The prevention of over-specialisation, as we have already 

 seen, should be the aim of all organisation, of all genuine 

 adaptation. It is as important as the prevention of disease. 

 An organism can remain fully alive to the contingencies of 

 existence only if it maintains a sufficiency of fruitful 

 symbiotic correspondences. 



Those parts of plants which show so considerable a power of dis- 

 charging each others' offices, are not widely unlike in their minute 

 structures. And the tissues that in animals are to some extent mutually 

 vicarious, are tissues in which the original cellular composition is still 

 conspicuous. But we do not find evidence that the muscular, nervous, 

 or osseous tissues are able in any degree to perform those processes 

 which the less differentiated tissues perform. Nor have we any proof 

 that nerve can partially fulfil the duty of muscle, or muscle that of 

 nerve. We must say, therefore, that the ability to resume the primordial 

 community of function, varies inversely as the established specialization 

 of function ; and that it disappears when the specialization becomes 

 great. 



There is, of course, no need in a "high" organism to 

 resume the primordial community of function for ordinary 

 purposes, for the simple reason that it is now adapted to bio- 

 economic purposes of quite a different degree from that pre- 



