A MUTANT OF THE OLD ENGLISH 



RAT 



F. A. E. Crew 

 Animal Breeding Research Department, University of Edinburgh, Seotland 



WILD white rats were reported 

 in certain warehouses in Bris- 

 tol in 1920, and a well-known 

 fancier, Mr. H. C. Brooke, of Taunton, 

 took steps to secure live specimens. He 

 expected to obtain feral fancy fats 

 (Mus norvegicus) , but to his great as- 

 tonishment the rats he received were 

 all black-eyed, creamy- white specimens 

 of Mus rattus rattus, the Old English 

 Black Rat. He ultimately obtained two 

 Black-eyed Whites, and two Black-eyed 

 Fawns, one of the latter being sexually 

 immature : all four were males. A 

 pregnant black-eyed pale- fawn female 



was caught, and still another black- 

 eyed white was reported to be in the 

 hands of a fancier of Bristol. Accurate 

 information as to the number of the 

 rats seen before Mr. Brooke heard of 

 them is not available, and it is not 

 known whether such rats are still to be 

 found in the locality. 



Below are given the results of the 

 breeding work carried out by Mr, 

 Brooke. Since the discovery and first 

 description of this new variety of Mus 

 rattus rattus were made by him. I pro- 

 pose to give ths name Mus rattus rat- 

 tus var. hrookei to it. 



Table I— Crosses of the Wlute Mutant Rats Made by Mr. Brooke. 



Parents 



Offspring 



Black 



hrookei 



agouti 

 $ 9 



1. hrookei (w) X wild black 4 



2. brookei (w) X wild white-bellied agouti.. — 



3-6. brookei (w) X Fi from (2) 1 



.7. trrookei (f) X wild yellow-bellied agouti.. — 



8. brookei (f) X Fi from (7) — 



9. brookei (w) X wild black (extracted).... — 

 10. brookei (w) X heterozygous black '■) 



— 7 ( w ) 3 ( w ) 



2(f) 

 6 ( w ) 



?> (f 



5 + 



(w) — — 



w, white; f, fawn. *Mr. Brooke reported that some of these were white- and others 

 grey-bellied ; 4- that some were grey- and others yellow-bellied. 



Table II— Results of Breeding Work Witli White Mutant Rats in the Animal Breeding 



Research Department 



Parents 



Offspring 



Black brookei (white) 



5 9-59 



1- 4. brookei (w) X wild black 13 18 — — 



5- fi. Fi from ( 1-4 ) X Fi 4 6 2 — 



7-12. /7 roo/^r / (w) X Fi from (1-4) 10 8 12 3 



221 



