92 



BIOLOGICAL LECTURES. 



from the Austrian caves, placed in the sunlight, and in the 

 course of a month becomes darkly pigmented, there are two 

 interpretations of this pigmentation : either that we have 

 revived a latent character, or that we have created a new 

 character. The latter interpretation can alone be taken as a 

 proof of Buffon's factor when it is found to be followed by- 

 hereditary transmission. 



Poulton,! as a supporter of Neo-Darwinism, takes this view, 

 in reply to Beddard and Bateson, and as an induction from his 

 beautiful and exact experiments upon the coloring of lepi- 

 dopterous larvae. After producing the most widely various 

 colorings and markings by surrounding the larvae during on- 

 togeny with objects of different colors, he urges that the 

 changes thus directly produced simply revert to adaptations to 

 former conditions of life, in other words, that they are palin- 

 genic. Whether this interpretation is correct or not, Poulton 

 proves that, no matter how stable certain hereditary characters 

 may appear to be, repetition in ontogeny depends upon repe- 

 tition in environment, and that there are wide degrees of 

 ontogenic variations which do not become phylogenic at least 

 in several successive generations. 



From many other analogous researches we gather the follow- 

 ing principle to which far too little attention has been paid in 

 the study of the phenomena of variation in their bearing upon 

 the factors of evolution : // is that ontogenic repetition depends 

 largely upon repetition in environment and life habit, while 

 ontogenic variation is connected zvith variation in environment 

 and life habit. If the environment be changed to an ancient 

 one, then ontogenic variations tend to regression or reversion 

 (i.e., palingeny) or practically to repetition of an ancient type. 

 It is necessary to state clearly that there is practically con- 

 clusive evidence for such a principle, not only in the later 

 stages of development, as in the respiratory metamorphosis of 

 the Amphibia, but extending back to very much earlier stages 



1 E. B. Poulton : Further experiments upon the color-relation between certain 

 lepidopterous larvae, pupae, cocoons, and imagines and their surroundings. Traits. 

 Ent. Soc, pt. IV, p. 293. London, 1892. (Contains a reply to Beddard and 

 Bateson.) 



