300 Heredity of Melanism in Lepidoptera 



to whether the heredity of melanism in these insects follows definite 

 rules, and especially as to whether it follows Mendelian Laws of 

 Heredity. 



In the literature bearing on the subject records are to be found of 

 the breeding by entomologists of many thousands of moths which have 

 melanic forms, but the accounts are very seldom of such a nature as to 

 allow inferences to be drawn as to whether the heredity is Mendelian 

 or otherwise. 



In 12 species definite investigations have been made or are being 

 made: 



1. Spilosoma luhricipeda. The experiment of Mr J. Harrison^ on 

 this species and its melanic variety zatimo, Cramer (= var. radiata, 

 Haworth), and other experiments made here 2, and abroad^ seem to 

 show that there is no complete dominance, but by selective breeding 

 pure strains of the melanic forms have been obtained, and an interesting 

 point is that these forms become larger and stronger than the type, and 

 double-brooded. 



2. Aplecta nehulosa. Experiments have been carried out by 

 Messrs Mansbridge, Harrison and Main (see table), and to my mind 

 prove that melanism is a Mendelian dominant ; and a point of special 

 interest is that the homozygous and heterozygous forms are probably 

 distinguishable. In the first instances it seemed certain that the 

 melanic variety thoivpsoni, which is black but has white terminal area 

 (i.e. wing margin and fringes), is the homozygous form ; and the melanic 

 variety rohsoni, a dark suffused form, at times almost black, but never 

 with white terminal area, is the heterozygote. 



Mr Mansbridge now considers it likely that only those specimens of 

 rohsoni which have grey scapular areas are the heterozygotes and 

 hopes to settle the question by experiments now in hand. 



Of the 10 families recorded in the table, only one, the last, fails to 

 support the assumption that melanism is dominant, the fact that 

 13 type specimens appeared seems to show that both parents are 

 heterozygous, which is not impossible, as entomologists differ as to the 

 exact differentiation of the two melanic varieties, thompsoni and 

 rohsoni; and unless the specimens are in perfect condition it is most 

 difficult to decide. 



1 Entomologist, 1893, pp. 65, 247, 346 ; 1894, pp. 95, 129, 205. 



« Naturalist, 1894. W. Hewett, p. 253. 



3 Standfuss, Handbuch d. Gross -Schmetterlinge, 1896, p. 307. 



