Elmer on Growth and Inherilance 441 



as in itself self-evident, that physiological changes must always pre- 

 cede morphological changes of structure in the organic world, because 

 the former dttermines the latter. ^ 



The significance of this, taken in conjunction with other 

 [assertions, will appear later on. 



In considering the effects of temperature, some interesting 

 facts noticed by Dorfmeister are described.^ This observer 

 has 



* ever since 1845 made experiments on the effect of temperature in 

 the colour and marking of butterflies. He explains first of all that 

 through many years' experience in rearing caterpillars, he has been 

 convinced that the production of varieties of butterflies depends much 

 more on climatic conditions, in which temperature is a chief factor, 

 than on either food or hybridisation. Dorfmeister learns from his 

 experiments that temperature exercises the greatest influence on the 

 ■colour and markings of butterflies when it acts upon them during the 

 change into the pupa, or shortly afterwards. In many, a rise of 

 temperature produces a lighter, more brilliant ground colour, a fall a 

 darker or less brilliant ; for example in Vanessa, lo, Utricae, etc. In 

 Jyupressia Caja the red-yellow ground colour of the posterior wings 

 is changed by a rise of temperature into vermilion- red ; by a fall, into 

 ochre-yellowj' 



The specially stimulating effects of surrounding colours is 

 Tery curious, and has been Avell worked out by Mr. Poulton 

 of Oxford. As Eimer says, pupae have assumed the red 

 colour of a cloth investing them, a colour to which they 

 could scarcely be exposed under natural conditions, and to 

 which in any case they could not have been adapted by 

 selection. Well may he say,^ ' Many really wonderful cases 

 of adaptation, apparently due to selection, probably come 

 under this category,' a category including such cases as the 

 common frog, which changes its hue according to the colour 

 of the ground, not rapidly, but gradually. 



The power the frog has of thus changing was experi- 

 < mentally ascertained by the Professor : — 



1 P. 131. ^ P. 144. ' 



