44 



SCIENCE-GOSSIP. 



few special phenomena that have proved interesting 

 to me. 



Origin of Varieties or Local Races. 



We may make the general statement, subject to 

 the above limitation, that uniformity in environ- 

 ment tends to produce a general uniformity in the 

 species ; whilst great differences of environment 

 tend to produce great differences in the species. 

 Many species of Lepidoptera bearing out this 

 general statement, will occur to all entomologists, 

 yet it is not difficult to mention species whose 

 appearance suggests antagonism to the general 

 principle here enunciated. 



The well-known Pyrameis cardui has an almost 

 cosmopolitan range. It exists under a variety of 

 physical and climatic conditions in both the Old 

 and New World, yet it is a species that varies 

 little. As a matter of fact, in spite of the apparent 

 dissimilarity of its habitats, these are comparatively 

 alike. The species inhabits the sub-tropical and 

 warmer temperate regions of the world. Hence 

 the climatic conditions are not unlike. From 

 these areas it is a wanderer, and has no lasting 

 habitation in the colder regions, of which it is 

 reported to be a native. Its habits are similar all 

 over the world. By the swiftness of its flight it 

 escapes from its enemies, and, on a flower-head, 

 at rest, it is sufficiently protected to be difficult of 

 detection. Variation in its colours would be of no 

 service to the species ; hence, in spite of its wide 

 range, there is no attempt to set up local colour 

 variation. The Australian form, keyshaud, shows a 

 tendency to develop a transverse row of ocellated 

 spots on the hind-wings. Now and again a 

 striking aberration may be bred or captured, but 

 these do not amount, perhaps, to one in a million, 

 and do not affect the general question. Here, 

 then, we have an instance of a species in which 

 variation in hue would be of little or no use to it, 

 and we find as a result that its colour and markings 

 are very rarely modified, whatever may be the 

 conditions of its environment. 



Let us now consider for a moment, a species 

 that depends not upon its swiftness of flight, but 

 upon its colour and markings, for its safety. No 

 better example can be selected than Aniphidasys 

 betiilaria. Its pale grey-white colour, plentifully 

 peppered with black dots, forms about as useful a 

 pattern as one can well imagine for the protection 

 of this species. On the tree-trunks on which it 

 rests, its colour and markings are its salvation. 

 Yet its colour would be fatal on the black fences 

 and tree-trunks to be found in all manufacturing 

 districts. In these districts, natural selection has 

 eliminated the pale conspicuous forms, and a 

 melanic form known as the var. doiibledayaria has 

 been evolved in its place. The process of evolution 



has been exceedingly simple, just the weeding out 

 of the most conspicuously pale specimens, and the 

 retention of the darker and less conspicuous forms. 

 The same process of selection has taken place 

 in the formation of the melanic aberrations of 

 Teplirosia crepuscularia, T. bistortata, Dhirnaeafagella, 

 and numbers of other species. Utility is the 

 mainspring of the formation of ail these melanic 

 forms. The physiological factors of variation 

 necessary for the production of this result were, 

 and are, present in all these species. They possess, 

 in their typical forms, black and white scales in 

 varying numbers ; utility has seized on the useful 

 character, and has moulded the material at its , 

 disposal into its own channels for the advantage 

 of the species. 



Again, let us examine a species like Gnophos 

 ohsairata. This species, as all lepidopterists are 

 aware, rests upon the ground, and is entirely 

 dependent for its protection on the resemblance 

 which its colour bears to that of the rocks upon 

 which it rests ; and this resemiblance is perfect — 

 black on peat and dark slate, grey on limestone, 

 white on chalk, with such a nice gradation in tint, 

 corresponding with that of the different rocks upon 

 which the species is found, that one can almost 

 tell exactly where individual specimens have been 

 captured. Here, the part that utility has played 

 in the determination of the various local races of 

 this species is obvious. 



I do not here wish to enter into the physiological 

 processes involved in the development of these 

 local forms. I only want to point out that they 

 have been developed, because the points which 

 distinguish them from each other and the type, 

 are severally useful to the species, under those 

 conditions of environment by which each indi- 

 vidual form finds itself surrounded. The modifi- 

 cation of many of the species here incidentally 

 referred to — Amphidasys betidaria, etc. — in the 

 direction of melanism is largely connected with 

 certain habits that these species possess in common. 

 The phenomenon, too, is undoubtedly of compara- 

 tively recent occurrence, and has largely increased 

 within the last fifty years. That the phenomenon,, 

 as exhibited by these species, has been brought 

 about by changes in the environment, must be 

 obvious to all who will only look for them. The 

 modification of other species — Gnophos ohscurata^ 

 Dasydia obfuscata, Agrotis lucernca, etc. — with a 

 slightly different habit, sometimes, in a somewhat 

 similar direction, is of much greater age, and dates 

 back, probably, as long as the species have rested 

 on differently coloured rocks in different localities. 

 Still, the hand of utility is just as evident here, 

 as in the previous cases. What is true of the 

 formation of these local races, must be true in 

 a measure of species themselves. 

 (To bd continual.) 



