700 Mr. R C. L. Perkins on the 



get by selection a melanic form from a pale creature. If 

 it is then placed under exactly similar conditions to those 

 of the parent pale form, it is certainly likely to revert, but 

 if it is, as probably would be the case in nature, maintained 

 for generations, it seems to me the whole life of the 

 creature would be profoundly modified, and germ-cells 

 and many other parts would be affected. Many import- 

 ant external agencies would be changed, absorption of 

 heat, e. g. They seem to expect to see everything revert, 

 because it is known to do so in a limited number of 

 examples and after a few generations. 



One of the most important parts of my introduction 

 will deal with insects known to have been introduced. 

 Some of these produce a brood every three weeks or so 

 throughout the year. Is it not remarkable that after 

 years in the islands, and having come from very different 

 countries, we do not find these producing varieties under 

 such new conditions, and after so many generations ? 



It seems that it ordinarily takes a great time to start a 

 variable condition, but it does come in the end, for, if we 

 look at the species which are peculiar to the islands, but 

 are comparatively recent arrivals (i. e. not very peculiar 

 and which have not yet given rise to allied species), we 

 see that these are almost always excessively variable. Con- 

 sider how constant are the undersides of Vanessa atalanta, 

 cardui, etc., yet our V. tammeamea, Esch., allied to these, 

 presents the most remarkable variations constantly. 

 Hypenodes altivolans, hardly different from a species found 

 in England, New Zealand, etc., is extraordinarily variable 

 with us, and the same is true of many other Hawaiian 

 species. 



Nov. 15, 1911. 



I am much impressed with the stability of species for 

 many generations under changed conditions — to which I 

 have referred previously. 



Of course a species already in a highly plastic condition 

 would presumably be more likely to exhibit change in a 

 short time. But — 



(a) In Blackburn's collection (of which I have a large 

 part), formed thirty years ago, variable species 

 exhibited the same varieties then as now. 



(I) Introduced species from other very diverse countries 

 have not altered after many generations. This 



