434 SECTIONAL TRANSACTIONS.— D. 



possibly by oxidation. (5) By dilution and different rate of pigment 

 deposition the bluer ' purple ' eye-colours are obtained. 



It is interesting to note that the eye-colours of other Drosophila species, 

 though the wild type may be different and may possibly correspond to a 

 mutant of D. melanogaster, show a similar range of variation. This point 

 is illustrated by genotypes obtained from inbreeding wild populations of 

 D. subobscura. 



The wild type body colour of D. melanogaster is yellow with black stripes 

 on the abdomen and a certain amount of black pigment on the thorax and 

 bristles. In ' yellow ' the black pigment is reduced in amount, the stripes 

 on the abdomen are light brown, there is no diffuse black pigment on the 

 thorax, and the bristles are light. In ' black ' and ' ebony ' the yellow colour 

 is covered by black. In the combination ' yellow-black ' the animal has 

 a yellow ground colour with a dusting of black. 



Several forms of dilution have been found in the nearly completely black 

 D. subobscura. As a yellow mutant has been found, it is clear that this 

 species is capable of forming a yellow pigment, which is hidden under the 

 strong concentration of black colouring matter. 



Dr. J. N. PiCKARD. — Rabbit coat-colours. 



The demonstration of rabbit pelts has been arranged to show how a know- 

 ledge of genetics can be used for practical purposes in animal husbandry. 

 In the centre of the top row of pelts is an ' agouti ' or wild rabbit fur, which 

 is the original colour. To the left and right of this are pelts showing colour 

 mutations. Combinations have been made between these mutations and 

 as a result the pelts of the lower row have been produced. For example, 

 it is expected that on crossing a ' black and tan ' rabbit (a'B C) to a ' chin- 

 chilla ' (A B c'^*') and inbreeding the offspring, that one ' silver fox ' (a*B c"^^) 

 would be produced amongst every sixteen youngsters bred. It, mated to 

 its like, would breed only ' silver foxes.' 



There have been produced varieties of rabbits whose pelts when made up 

 closely resemble almost all of the rarer fur-bearing animals. The demon- 

 stration shows, by means of coloured ribbons, the crosses which can be 

 made in a number of such cases, although, for lack of space, the shortest 

 method of producing a new variety is not shown in all instances. In addi- 

 tion to the normal coated pelts, ' Rexes ' with plush-like furs, and ' Angoras ' 

 with coats measuring up to ten inches or more in length, can be ' made ' 

 in any colour. 



Mr. M. S. Veas^.— Yellow fat in Babbits. 



The colour in rabbits with yellow fat is due to xanthophyll absorbed from 

 the green food. Rabbits with white fat have in their livers an enzyme which 

 breaks down the xanthophyll. The presence of this enzyme is determined 

 by a dominant gene ; in its absence the enzyme is not formed and xanthophyll 

 is deposited in the fat. 



Prof. R. C. PuNNETT, F.R.S. — Colour in Budgerigars. 



The principle colour varieties depend upon genes affecting amount of 

 melanin, production of a lipochrome and alteration of feather structure. 

 Of the three allelomorphs affecting melanin production, Rr produces the 

 normal intensity, Rg the reduced amount shown in * grey- wing ' types," 

 and Rp the ' pallid ' forms. The dominant L produces a yellow lipochrome ; 

 interaction with the R series gives various shades of green. When the 



