176 LECTURES ON BIOLOGY 



the blind play of chance ; it is, moreover, the only way to com- 

 prehend the wonder of organic formation. The assumption of 

 inner factors of evolution could only then be justly described 

 as mysticism if we represented these inner forces as something 

 absolutely incomprehensible ; but there is not the least cause to 

 do this. To these inner forces the psychic energy there applies 

 the same demand, as to all other forms of energy, that they must 

 be capable of being determined quantitatively. That it is still 

 beyond the powers of science to do so is no proof to the contrary. 

 One must agree with Pauly when he raises the objection against 

 the theory of selection that logically it turns matters upside down 

 by making reproduction the causa causans of the acquisition of 

 fitness ; as a matter of fact the organism must first have acquired 

 fitness by fulfilling certain conditions of its existence before it 

 can proceed to reproduction. 



That species will remain unchanged for unlimited periods if 

 the conditions of their life remain unchanged is conclusively 

 proved by the inhabitants of the deep seas. At vast depths 

 in which no change has taken place since times immemorial, we 

 still find the same forms which we also know as petrefacts 

 from the oldest geological formations. A brachiopod, Lingula, 

 has to-day the same appearance as its ancestors in the Silurian 

 strata. The crinoids, or 'feather-stars,' which live in shallow 

 water near the surface, differ from their geological ancestor 

 Pentacrinus, or sea-lily, in numerous points ; above all, they 

 are free-moving, whilst sea-lilies are fixed on the ocean bed. 

 But the history of their evolution proves their origin beyond 

 doubt, for the crinoids have a fixed Pentacrinus stage. The 

 venerable sea-lilies were long thought to be extinct. The 

 surprise was, therefore, all the greater when recently there were 

 found on the ocean bed crinoids which exactly resembled their 

 ancient ancestors. (Compare coloured plate II.) 



Another difficulty of the theory of selection is that generally 

 the variations are far too slight and of far too little advantage 

 to the animals which exhibit them to be regarded as being of 

 real value in breeding. To mention again the instance of the 

 hare, snow-white varieties do not appear among the brown 

 animals all at once, but according to the theory of selection 

 we are to assume that first there appear a few individuals 



