A. H. Sturtevant 46 



As is shown above they do produce a trifle less than 10 "/^ blacks. I 

 am still convinced, however, that there is something in my original 

 hypothesis. It could scarcely be a coincidence that twenty brown 

 sires should be heterozygous and none homozygous, if we except the 

 Thoroughbreds. Among the latter I believe that Wolfs Crag, Desmond, 

 and perhaps Ladas are heterozygous, for it is evident that in a population 

 containing only 1 °l^ recessives there would not be a large proportion 

 of heterozygous mares, and a heterozygous stallion would of course 

 not produce recessives when mated to pure dominant mares. Again, 

 it will be noticed in the tables above that, excluding chestnut foals, 

 black mated to bay gives only 16% black foals, while black mated 

 to brown gives 33 7o> or twice as many. And while brown to brown 

 gives only 10°/^ blacks, bay to bay gives still fewer — only about 1 %, 

 or 3 7o> i^ w® omit the Thoroughbreds, of which the table illustrating 

 this class has a relatively large proportion. 



According to Wilson's hypothesis that brown is dominant to bay, 

 bay to bay should produce no browns. This would require the further 

 hypothesis that the 205 browns recorded from such matings are errors 

 in description, which certainly does not seem to me to be probable. 

 Again, there should be some brown sires producing no bay foals, but 

 as a matter of fact all of the 25 brown sires found produce a large 

 proportion of bays. I have, in fact, never yet found a sire which did 

 not produce bays. Finally, as stated above, I am unable to agree with 

 Wilson that bay and brown can be satisfactorily separated. I base 

 this upon my own observation, upon the frequent changes from bay 

 to brown and vice versa which he mentions finding in the Clydesdale 

 records, and the similar changes which I have observed among Harness 

 Horse records, and upon the frequent recording of English Thorough- 

 breds as "bay or brown." My conclusions, then, are that brown and 

 bay are not distinct, brown being merely a dark bay, and that brown 

 is more often CHBb than CHBB, and never CHbb. It would be 

 interesting to know whether or not the heterozygous bays are darker 

 than the homozygous ones. 



In regard to gray there is no great difficulty. I thought when I 

 published my first contribution that I had a non-conformable case, 

 where two brothers not gray were siring about 50 % gray foals. One 

 of these, Dispute, I now know to have been wrongly recorded, as his 

 owner, Mr John Taylor, and another breeder, Mr W, B. Gill, both write 

 me that he is a gray. The supposition therefore is that his brother 

 was also a gray, though I have been unable to verify this. But if he 



