ORTHOGENESIS 345 



closely related to wrong feeding, how clandestinely a negative 

 and eventually pathogenetic direction may be given to evolu- 

 tion. It follows that we must study the nutritional past of a 

 species and the correlated changes of form and of use-related- 

 ness in the web of life to discern the prevailing direction which 

 the consequent slow and gradual metabolic developments have 

 given to its evolution. 



Prof. Eimer tells us that butterflies are known " on whose 

 colouring and markings the food of the caterpillars has great 

 influence." 



I have special grounds for the conviction that many new species 

 have arisen through the caterpillars having been at one time or another 

 forced to accommodate themselves to a change of food. In evidence of 

 this is the fact that numerous very slightly differing species of Vanessa, 

 e.g., F. polychloros, V. xantho mel.as, V. album, and F. urticce, lay their 

 eggs on different plants. It is natural to infer that in such cases the 

 difference in the quality of the food has been the cause of the origin 

 of different characters. 



This bears out in part my thesis as regards the importance 

 of nutrition in evolution, and likewise my proposition that all 

 animal development can be studied duly only if that of the 

 connected flora is simultaneously taken into account, for it is 

 obvious that one part of the hereditary mechanism of these 

 butterflies lies outside their own organisation. The same must 

 be said of some of the observations of Gabriel Koch on the 

 Variation and Formation of Species in Lepidoptera, as 

 instanced by Prof. Eimer. 



A change in marking is easily produced by a change in the plants 

 fed upon (the "bear" and other species). 



Nocturnal species which live exclusively on conifers have dull 

 colours, usually grey, as for example our pine hawk-moth (Sphinx 

 pinastri), or the pine-spinner (Gastropacha plni), and several foreign 

 species. This is so invariably true that Koch was able to conclude 

 from the colours of certain species from Sydney and Baltimore that 

 the caterpillars lived upon coniferous plants, and when he suggested 

 that they should be sought on such plants his conclusion was found 

 to be correct. 



It is known, Koch says, that when the caterpillars of our German 

 "bears" (Chelonia s. Euprepia caja) are fed from their hatching to 



