300 nEroRTs on the state ov science. 



reseuiblaiioc lo a wild grey. No mice of other colours appealed in this 

 litter, but the number of young is too small to permit the conclusion that 

 the female parent is homozygous for yellow. 



(ii.) With a chocolate yellow, giving two yellows (colour of young) 

 and one black. 



(iii.) With another chocolate yellow ( J 44) giving four yellows (of 

 which one died before adult condition was determinable and the other 

 three developed dark pigment) and one black. 



Including the various kinds of yellows under one category, and 

 summarising the results of matings involving yellow mice, I find that, 

 so far, no yellow mice have certainly proved homozygous ; that the result 

 of mating yellow with yellow has been to give nine yellows and five of 

 the recessive colour (black) ; and that matings of yellow with another 

 colour have given twelve yellows and eight of the recessive colour. 



(b) In addition to the yellow mice I obtained mice of other colours, 

 of which pure races are necessary in order to test at all adequately the 

 gametic constitution of the yellows. 



(a) Chocolate mice. — These are particularly useful for testing pur- 

 poses, as their colour is recessive to all others. Some chocolate mice 

 were therefore obtained from various fanciers and tested. In all cases 

 only chocolate has resulted from mating chocolate with chocolate. A 

 large number of chocolate mice is desirable. 



(b) A pair of blues were obtained from a fancier, and when mated 

 together gave seven youngsters, all blues. Various blues have also 

 appeared in mating black with black. 



(c) Some blacks also were bought. Some of these were found to 

 contain blue recessive ; by appropriate breeding a race has been obtained 

 which promises to breed true to blackness. An interesting result of 

 mating black with black has occurred in one instance— the pair in 

 question giving three youngsters which at sixteen days old are one of 

 them black, one blue, and one chocolate ; the matter is being investigated 

 further. 



(d) For greys I am using wild house mice. I shall also endeavour to 

 obtain a true-breeding extracted race. 



I refrain from discussing these initial results in detail until more 

 material is to hand, as this would require an undesirable degree of 

 speculation. For the present it is sufficient to point out — 



1. That five of the six yellow mice which have so far been mated have 

 proved to be heterozygous in respect of coat colour, in accord witli 

 Cuenot's result. The exceptional case of ? 19 is considered in section (i.) 

 above. 



2. There is nothing to contradict the order of dominance of the 

 various colours as found by other investigators. In particular yellow 

 is dominant to all other colours. 



3. The occurrence of black, blue, and chocolate in one litter from 

 a mating of black with black. Also the apparent presence in the 

 recessive condition of both black and blue in g 45 yellow. 



4. The advisability of further classification of the various adult forms 

 included under the term ' yellow,' and whose first coat is light yellow. 



It will be seen that the experiments are at present in an initial 

 stage — that the interesting stage is just being reached. Thus the 

 clear yellow mice are in the third generation ; pure races (so far as 

 tested) of chocolate, blue, black, and grey have been obtained for 



