] 6 Scientific Proceedings, Royal Dublin Society. 



Thus, among every sixteen calves, the progeny of Dexter with Dexter, 

 there ought to be 



12 sliort-legged animals, 9 of tliem black, and 3 of them red ; 

 4 tall animals, 3 of tliem black, and 1 of tliem red. 



Of the sixteen animals only four — those underlined — are absolutely pure 

 for both form and colour. Two of these four are new pure types — 

 tliose underlined twice. The others are all hybrids in respect of either 

 foi-m or colour, or both. An inspection of the diagram will show. 



That is to say, 16 Dexter cows mated with Dexter bulls ought to 

 produce 9 black Dexters, 3 red Dexters, 3 black Kerries, and 1 red Kerry. 

 But they do not do so. A number of the Dexters are misshapen and 

 useless.! The proportion cannot be stated with accuracy. According to 

 some breeders it lies somewhere between 25 and 50 per cent. Assume it to 

 be 33 per cent. Then four of the twelve Dexters referred to above are 

 useless. Thus, by mating his 16 Dexter cows witli Dexter bulls the 

 breeder gets only 4 Kerry calves and 8 Dexter calves — the other 4 being 

 useless — wliereas, by mating them with Kerry bulls he would get 8 Keny 

 calves and 8 Dexters. The same result would be got by mating Kerry cows 

 with Dexter bulls : and in both cases the calves produced would be black. 



This can also be shown diagramatically. The hybrids or Dexters are 

 represented, so far as size is concerned, by ,, and the Kerries by ,. When 

 these two kinds are bred togetlier, their progeny are one half sliort, one half 

 tall. Thus : — 



^^\;^* . 8 s t t 



Aud since the Kerries are all black, and black is dominant over red, the 

 progeny of pure Kerries and Dexters must all be black. 



Of course it may still be possible to eliminate the hybrids that have to do 

 with the production of misshapen calves, as it is also possible to find out 

 which of the Dexters ai'e pure for both colour and shape, and then breed 

 pure Dexters from them. To do these things, however, experiment, means, 

 and patience are required. 



As these misshapen calves may be interesting to students of Mendelism, 

 let us indicate where they may be looked for. A breeder of experience tells 

 us they are always black. The three pure black animals among the Dexters 

 may therefore be suspected. 



1 For a description of these calves, see Dr. C, G. Seligmann's paper on "Cretinism in Calves," in 

 t;he Journal of Pathology and Baclerioloffi/ for March, 1904. 



