( io ) 



fresh stage of growth in our comprehension of at least one 

 portion of the evolutionary domain. And the peculiar value 

 of entomological data for research on Darwinian lines was 

 speedily recognised. The material with which we entomo- 

 logists have to deal is for the most part abundant, of manage- 

 able size, easy of manipulation, and favourably constituted for 

 experiment. Hence it has followed that many of the most 

 important steps in the progress of our evolutionary knowledge 

 have depended directly or indirectly on the study of insects. 



Let me take as an example the present state of scientific 

 opinion with regard to the transmission of acquired char- 

 acters, or, as some prefer to put it, the inheritance of somatic 

 modifications. It is hardly necessary for me to say that 

 neo-Lamarckians are still on the look-out for an instance of 

 such transmission, and that neither among insects nor any- 

 where else have they been able to find one. The antecedent 

 improbability of the alleged phenomenon has been well 

 shown by many writers, and by none more convincingly than 

 by Professor Poulton, in one of the admirable Presidential 

 Addresses delivered by him from this Chair. But the failure 

 of the neo-Lamarckians to establish the principle of specific 

 transmission must not blind us to the fact that the germ- 

 plasm is far from possessing the stability and inviolability 

 with which it was once supposed to be endowed. Weismann 

 himself, with great candour, admitted at a comparatively 

 early stage in his work that the germ-plasm was not in all 

 cases out of the reach of external influences. It is of special 

 interest to us as entomologists that lie was led to this 

 conclusion by experiments on a butterfly — the well-known 

 "Copper" (Chrysophanus phloem). Exposing pupae of the 

 northern golden-red form of this insect to an abnormally 

 high temperature, he found that many of the resulting 

 butterflies were slightly dusted with black. On the other 

 hand, pupae bred from eggs sent from Naples, which would 

 under ordinary circumstances have produced butterflies of the 

 dark southern summer form, were subjected to a relatively 

 low temperature and gave rise to perfect insects in which the 

 normal dark coloration was sensibly diminished. These 

 results, as we shall doubtless all remember, agree with those 



