NAGELPS VIEW 15 



plex structure, greater division of labour. Distinct from this 

 perfection of organisation there is a perfection of adaptation, 

 " which is repeated at every degree of organisation, and which 

 consists in the organism having, in relation to the external 

 conditions at the time, the most advantageous structure which 

 is compatible with its degree of complexity and the division of 

 its functions.". 



The improvement of structure and the division of labour 

 progress according to this conception within certain lines 

 uninterruptedly, on account of the mechanical activity, 

 following certain laws, of the living organic substance ; and 

 this course of things is only so far affected by other influences, 

 that the external conditions of each particular period by means 

 of adaptation favour those arrangements of structure which are 

 most useful in the struggle for existence. 



Continual advance of its own accord towards perfection is 

 thus, according to Nageli, a property of living organic substance. 



But as Weismann's germ-plasm, unaffected by all external 

 influence, would have been gradually used up, so it seems to 

 me, according to Nageli's principle of improvement, since it 

 has been constantly at work ever since there have been living 

 beings at all, the lowest creatures which existed millions of 

 years ago must long ago have changed into higher there 

 could no longer be any lowly-organised simple living things 

 at all. Nageli explains their existence by the assumption 

 that abiogenesis still takes place at the present day. The 

 origin of the organic from the inorganic, he says, is a con- 

 clusion to be drawn from observation and experiment, a 

 fact which follows from the law of the indestructibility 

 of matter and energy (a sentence which, excepting the 

 words " is a fact," shall not be contradicted). To deny 

 spontaneous generation, he says, would be to proclaim a 

 miracle. "In later times, and now still, abiogenesis must every- 

 where occur where the conditions are the same as in the 



