136 



SCIENCE-GOSSIP. 



nutritious, and vice versa, and thus leaving them 

 with an insufficiency or excess of energy for the 

 production of an imago of normal size and 

 pigmentation, (2) causing less or more rapid 

 meta;bolism of the pupal tissues during the period 

 at which the imaginal tissues are being perfected 

 — really affect any species of Lepidoptera at all. 

 Certainly it does not do so in the direction of 

 producing real structural modifications. 



Food AND Specific Characters. 



When writing "Melanism and Melanochroism 

 in British Lepidoptera," I stated that food could 

 not produce changes in the colours of insects. I 

 have long since retired from this untenable posi- 

 tion, although unable to give, off-hand a single 

 illustration from nature where food, without 

 doubt, has caused a change in a species. Probably 

 the stunted moorland forms of Hypsipetes sordidata 

 and Cidaria nissata, with which Mr. Porritt has 

 made us acquainted, are due to the innutritions 

 nature of their food. I am also aware that ill-fed 

 larvae produce either dwarfed or ill-pigmented 

 imagines, the larvae evidently not being strong 

 enough, nor having reserve material and energy 

 enough, to produce the normal coloration. All 

 variations brought about by food, too, appear to 

 act in this direction, i.e. by increasing or decreas- 

 ing the amount of material available for wing 

 formation and pigment, and, thus, variations 

 produced by this means are those of size or 

 colour. In no way can these be considered as 

 hereditary, since they change with the substitu- 

 tion of a different food-plant with each brood, or 

 even part of a brood, if it be separated. Hence 

 these differences can in no way be considered as 

 specific characters. 



Sexual Selection in Lepidoptera. 



I have already (" British Noctuae and their 

 Varieties," vol. iii., p. 17) discussed sexual selec- 

 tion in its application to Le.pidoptera and must 

 confess that I am quite unable to subscribe either 

 to the views of Wallace or Darwin, that females 

 exert any real choice, or select the males with 

 which they pair. There may be some little 

 probability that sexual selection in a small degree 

 occurs in butterflies, but I have seen a female 

 Colias edusa paired whilst her wings have been limp, 

 and among the Lycaenids one must be a poor field 

 naturalist who has not seen wretched little males 

 in copulation with large and well-developed females 

 and vice versa, whilst dozens of well-developed 

 specimens are everywhere around. Among the 

 larger moths the males will often pair with the 

 females before their wings have fully expanded, 

 the females most certainly having exerted no 

 choice. Whatever influence sexual selection may 

 have on the formation of specific characters in the 



higher animals, I do not think such influence exists 

 in the Lepidoptera. Granted, however, the exis- 

 tence of sexual selection, then I fail to see how it 

 tends to the development of specific characters, 

 useful or useless. To me sexual selection appears 

 only as another phase of the general principle of 

 natural selection, and although I can see that the 

 picking and choosing of the females may stamp a 

 character already in existence in the males more 

 markedly on the race, I fail to see how it can 

 originate any new character for this selective 

 process to act upon. That the females would, as 

 a race, continue to pick males that possessed some 

 mark that had ceased to be of service to the species 

 is hardly conceivable. 



Isolation fixes Characters. 



I do not think that isolation can beget specific 

 characters. There can be no doubt that it tends to 

 fix, by natural selection, such characters as are 

 already in process of settlement. The tendency to 

 close interbreeding, the more constant character of 

 the environment to which the species is subjected, 

 and other similar causes, tend to define the charac- 

 ters more sharply when a species is strictly iso- 

 lated from the ancestral form. I have already 

 shown how isolation need not be a physical 

 isolation, like the separation of an island from the 

 adjacent continent, but that the emergence of 

 closely allied species at different times of the year, 

 by flying at different times of the day or night, or 

 by being restricted to different food-plants of local 

 habit, might be just as potent as separation by 

 physical barriers. 



Laws of Growth. 



Nor can the laws of growth originate specific 

 characters. The laws of growth, it appears to me, 

 must be applied to actual existent parts of an 

 organism, and until some nervous or other excit- 

 ing cause has been stimulated to bring about a 

 modification I do not see how the laws of growth 

 can influence any structure or organ. It appears 

 to be the case that only when other causes have 

 brought about changes useful to the species these 

 laws can have any action at all. 



Summary of Effects. 



It will be thus seen that I doubt entirely the 

 power of climate, food, sexual selection, isolation 

 and laws of growth to produce specific characters 

 at all, whether useful or useless. The modifica- 

 tion of parts necessary to bring about a new 

 specific character cannot be originated, I venture 

 to assume, by any of these phenomena. Climate 

 may alter the pigments of Lepidoptera, the scale- 

 structure, or the size of a specimen by its injurious 

 {i.e. abnormal) action on the larva or pupa ; but 

 none of these alterations are hereditary. Food, 



