MXTATION. 157 



pure for it, and therefore this peculiar state of things is perma- 

 nent in the family. By observing several pure-bred generations 

 of such material, the peculiar fact that all the females are 

 heterozygous, cannot be brought to light. A breeder of Silver 

 Wyandottes has no idea of the fact, that all his hens are hetero- 

 zygous for the gene which distinguishes his breed from Gold- 

 en Wyandottes. He does not know, that his silver hens pro- 

 duce as many germ-cells from which this gene is lacking, as 

 eggs having it. And at first sight it looks strange that all fe- 

 males of at least two different turtle-doves, and all females of 

 the domestic pigeon should be heterozygous for a gene, indispen- 

 sable for pigment-formation, and that their genetic constitu- 

 tion is such a one, as we would expect hybrids with one albino 

 parent to have. And yet, if we mate any silver-coloured hen to 

 a golden cock, we find that only fifty per cent of the off-spring 

 are silver, namely the sons : the daughters, being gold-coloured. 

 This curious inheritence was first brought to the notice of one 

 of us some fifteen years ago, when visiting the town of Assen- 

 delft in Holland. In the neighbourhood of Assendelft and 

 Landsmeer, the raising of ducks and fowls for eggs is an import- 

 ant industry. The common fowl in those regions is called As- 

 sendelver, and is practically identical with the Gold and Sil- 

 ver-pencilled Hamburg breed. For the production of pullets 

 that are destined to be kept for egg-production, the farmers 

 mate silver hens to golden cocks. The resulting chicks come 

 in two colours, white and yellow. Only the yellows, which will 

 ultimately prove to be all hens, are raised, and the whites, 

 which are cocks, are said to be destroyed. Later, one of us paid 

 a special visit to the neighbourhood to collect some data, 

 and found fourteen cases in which chicks were raised from 

 the combination of silver hens and golden cocks. 249 of these 

 were silver, and all males, and 243 were golden and pullets. 

 He found nine broods of chickens from two golden parents, 

 and all the 104 were golden. 



The other cross, golden hens and silver cocks produces chic- 

 kens of both colours in both sexes. He observed fifteen lots 



