TRANSACTIONS OF SECTION D. 515 
which has a melanic form, that segregation occurs, and that apparently melanism 
is a Mendelian dominant. 
In the well-known case of the common Peppered Moth, Amphidasys 
Betularia, where the melanic form, unknown till about fifty years ago, has in 
this period multiplied and spread all over England and is now far commoner 
than the type, it seems without doubt due to the facts that melanism in this 
species is a dominant characteristic, and that it carries with it a real but not yet 
fully explained advantage in the struggle for existence. 
Observations by various entomologists and a breeding experiment by the 
author also seem to point to Mendelian dominance, but the numerous inter- 
mediate forms obscure the issue, and at present complete experimental proof is 
not forthcoming. 
Observations on breeding the melanic forms of Aplecta nebulosa and Boarmia 
repandata by Mr. Mansbridge seem to show that melanism follows Mendelian 
lines in these species, but the evidence is not yet conclusive. 
With regard to the black form (Varleyata) of Abraxas Grossulariata, 
apparently the experiments have not been very extensive or prolonged, but it 
seems that in this species melanism follows Mendelian lines but is recessive. 
In a paper entitled ‘Melanism in Yorkshire Lepidoptera,’ read by Mr. G. T. 
Porritt to this Section in 1906, he makes observations on the breeding of Odont- 
optera bidentata and its melanic form, and the author is convinced from his own 
experiment that the results can all be reconciled with the Mendelian Law of 
Heredity. 
The author made the following experiment on Odontoptera bidentata :— 
In November 1909 pupz of both the type and melanic forms were obtained, 
and in the following April the imagines emerged and pairings were obtained of 
the pure strains and the resultant ova carried to maturity April 1911 (103 
specimens). 
From these, various pairings and cross-pairings were made, and 13 families 
raised (403 specimens), 1912. 
From these imagines further pairings and cross-pairings were made and 
34 families were raised, comprising 1,000 specimens, with the offspring of which 
the experiment is now being continued. 
Distinct segregation occurs, for although within both the type and the 
melanic forms there is a little variation in colour, there is no difficulty what- 
ever in distinguishing between them at a glance. No specimens occurred which 
could be called intermediate. 
The homozygous and heterozygous melanic forms are apparently indis- 
tinguishable to our eyes. 
It was also shown that extracted types breed as true homozygotes, and there 
are eight families to show that two heterozygous blacks, if paired, give 75 per 
cent. black and 25 per cent. type. 
All possible varieties of pairings have been made, and if 
MM=melanic (homozygous), 
Mm=nielanic (heterozygous), 
and mm=type 
the result in all the 50 families can be explained by the well-known Mendelian 
formule :— 
MMxMM=MM 
MMxMm=MM+Mm 
MM xmm=Mm 
Mm x Mm=MM+Mm+mM+mm 
Mm xmm=Mm+mm 
mmXmm=mm 
All the actual specimens (1,800 in number), which were bred in the ex- 
periments are exhibited. 
The author submitted with confidence that this experiment proves that 
melanism in this species is a simple Mendelian dominant. 
In the other species the evidence is not extensive, as the experiments which 
have been made have seldom been carried beyond the second or, at any rate, the 
third, filial generation. 
LL2 
