SUGGESTIONS FOR RELIABLE HYPOTHESES 167 



of the spring form, which, normally hibernates and is 

 therefore exposed to cold, be induced to develop by 

 artificial warmth, the summer form emerges, while 

 the chrysalis of the summer form, exposed to artificial 

 cold, yields the spring form. Thus the difference 

 between the Vanessa levana forms, which is rather 

 striking, would presumably originate through the 

 influence of warmth. 



Even the method of reproduction, as for example 

 with fungi, can be influenced by change of temperature. 



Another example is afforded by the Fireflies : these, 

 both in Germany and the Riviera, show two different 

 varieties which, as experiment has proved, are due to 

 warm influence. Since warmth generally accelerates 

 maturity, so we find, in snails, that the shell shows one 

 or more turns less under warm conditions, while cold 

 and a very favourable environment can defer maturity 

 and thus give the animals time to add under some 

 circumstances one or more spiral turns to the normal 

 number. 1 



Nutrition has also influence on the formation of 

 animals, independently of the directly detrimental 

 want of such. Thus the colour of many birds may 

 be altered by the kind of food given. 



The collective terms, indeed, such as midland, 

 or northern flora and fauna, etc., which indicate to 

 the botanist or zoologist a quite definite and objectively 



1 Deperet-Wegner : Die Umbildung der Tierwelt, p. 123. That is 

 very important for the judgment of palseontological finds, in which the 

 whole transformation is sufficiently often confined to the enhancement 

 of such deviations. 



