278 



NATURE 



[April 29, 1920 



Melanism in British Lepidoptera. 



TX/T ELAN ISM has long been a subject of special 

 ■»■''-*■ interest to British entomologists owing to the 

 rise and spread of melanic varieties in many British 

 species of moths and butterflies, such groups as the 

 Geometridae showing many examples. Records of 

 melanism go back at least to 1850, when the dark 

 variety Doubledayaria of Amphidasys hetularia ap- 

 peared near Manchester. It afterwards spread until 

 it became the prevalent or exclusive form in Lanca- 

 shire and the Midland Counties, extending also to the 

 Continent in later years. The earlier naturalists' 

 point of view (as represented by the writings of Tutt 

 and of Porritt) concerning its causation, related it to 

 the progressive darkening of the background in the 

 neighbourhood of cities as a result of industrialisation. 

 When this explanation was found to be inadequate, 

 moisture was added as a cause of melanism ; and 

 Tutt concluded that moisture would darken the sur- 

 faces of rocks in rural districts just as smoke darkens 

 surfaces in urban areas, natural selection progressively 

 favouring darker forms which habitually rested on 

 such darkened backgrounds. 



In a recent consideration {Journal of Genetics, 

 vol. ix.. No. 3) of melanism, based on extended 

 observations and breeding experiments in Yorkshire, 

 Mr. J. W. H. Harrison discards the older hypothesis 

 and proposes a new one. This is based on a modifica- 

 tion of the insect's metabolism by its feeding upon 

 substances more or less impregnated with chemicals 

 derived from the smoke. It is pointed out that certain 

 melanic areas, such as the vicinity of Middlesbrough, 

 Neweastle-upon-Tyne, and Moray Firth, are among the 

 driest in the country, having a rainfall of 25-28 in. Also, 

 in such species as Bocurmia repandata and Oporahia 

 dilutata the melanic varieties are confined to the 

 towns, while the type occurs in the surrounding 

 country. The melanic forms of . different districts, 

 moreover, differ from each other, showing that they 

 have originated locally and irrespective of each other. 



Observations showed that an increase in melanism 

 was accompanied by a striking decadence of cryj)to- 

 gamic plants, especially mosses, liverworts, and 

 lichens, many species having quite disappeared from 

 affected areas owing to smoke contamination. This 

 effect on vegetation, and also the degree of melanism, 

 is found to diminish as one leaves the town. 



Mr. Harrison compares melanism to such a_ condi- 

 tion as alkaptonuria in man. The latter condition is 

 known to be inherited, and may be considered a 

 chemical mutation in which the alkapton is not de- 

 composed owing to the absence of a certain enzyme. 

 He suggests that the taking in with the food of small 

 quantities of such salts as KCl, NaCl, and MnSO, 

 present on the foliage in urban areas would lead to 

 an increase in the amount of tyrosinase present, and 

 so to an increased deposition of melanin, since the 

 activity of various enzymes is increased by the 

 presence of small quantities of these salts. The same 

 interpretation is extended to melanic forms on coasts 

 and islands, where the vegetation is impregnated with 

 similar salts from the sea spray. 



It is known that in many cases melanic varieties 

 behave in inheritance as simple Mendelian dominants 

 to the type (e.g. Onslow, Journal of Genetics, vol. ix., 

 No. I, on the melanic variety of Boarmia (Tephrosia) 

 consonaria). In crosses with species of Oporabia, 

 however, the author obtained a blend which remained 

 true for two generations, and is interpreted as a 

 gametic blend, the melanism Ijeing of a perfectly 

 continuous type. Also, when the hybrids between 

 O. autumnaia and O. filigrammaria were crossed 

 back with the parent forms, a blend resulted. In the 



NO. 2635, VOL. IO5I 



F3 of the cross, however, a "pseudo-segregation" 

 was observed, which is likened to the behaviour in 

 Oenothera Lamarckiana. Many writers have sug- 

 gested such a relation between hybridisation and 

 mutation. 



In this interesting and manifold study the author 

 has discarded an original anti-Lamarckian bias, and 

 concludes that various cases, such as the food instincts 

 of O. filigrammaria and the period of emergence in 

 a pinewood race of O. autumnata, are only explicable 

 as true Lamarckian effects. Natural selection is 

 believed to lead to the genesis of local races, " limiting 

 the range of variation by the elimination of genetical 

 strains less protected in any given habitat." 



The haploid chromosome numbers are determined 

 for O. dilutata, autumnata, and filigrammaria as 30, 

 38, and 37 respectively, and the behaviour of the 

 chromosomes in meiosis furnishes a basis for a further 

 interpretation of the hereditary phenomena. 



University Developments at Manchester. 



T^HE University of Manchester is appealing for 

 -^ the comparatively small sum of 500,000^ in 

 order to enable it to maintain its present activities 

 effectively and to develop new features. These em- 

 brace not only additional buildings and equipment 

 urgently required for the extension of the School of 

 Medicine, especially in the departments of pharmaco- 

 logy and pathology, and for advanced scientific study 

 and. research in other important spheres of the 

 University's many-sided work, but also a large 

 increase in the professorial staff, including new pro- 

 fessorships in social and political science, physiological 

 chemistry, law, mathematical physics, and French. 

 The present Department of Commerce, established in 

 1904, is stated to be hopelessly inadequate to the needs 

 of a great commercial centre such as that of south- 

 east Lancashire, and demands, if it is to serve its 

 purpose worthily, a considerable strengthening of its 

 teaching staff. The University has recently estat>- 

 lished a new degree, namely, the doctorate in philo- 

 sophy (the Ph.D. degree), granted upon a course of 

 advanced study and research, which will necessarily 

 involve a large expenditure in staff and equipment. 



The University is committed to an expenditure of 

 a sum of 171,000/. in respect, among other items, 

 of the building and equipment of the new arts build- 

 ing, where it is intended to house the subjects of 

 languages, literature, history, and philosophy, the 

 endowment of new chairs, the reconstruction and 

 equipment of scientific departments, and the provision 

 of women's hostels. It is further contemplated to 

 set up a wide extension of extra-mural teaching so as 

 to bring the influence of the University more closely 

 in touch throughout its wide area with the needs 

 and aspirations of working people by means of exten- 

 sion lectures and systematic three-year evening courses 

 of tutorial classes. 



Already in response to the ap{>eal of the University 

 a Slim of about i6o,oooZ. has been raised, and it 

 ought not, having regard to the population and 

 wealth of the area the University serves, to be difficult 

 to secure the desired sum, and even more. With the 

 view of inducing a large number of people of small 

 means to participate in the effort to raise the money 

 required, a novel scheme has been launched in the 

 form of a prospectus, such as that issued on behalf 

 of limited liability companies, entitled "Lancashire 

 Development, Unlimited, The University _ of Man- 

 chester," inviting subscriptions fdr new capital to the 

 extent of 500,000?., divided into 425,000 cumulative 

 participating bonds of iL each and 1,500,000 people's 



