The progress of Genetics since the rediscovery of Mendel's papers. 377 



and also in certain colour-cases, of which the best known is that ot 

 the Andalusian Fowl. Here blue is the heterozygous type^), while 

 black and a peculiar white splashed with black are the pure types. 

 In this remarkable example we meet the fact that selection is 

 powerless to fix a type which is not represented in the gametes. 

 The efforts of fanciers have long been devoted to the attempt to fix 

 the blue type of Andalusian, but as the germ-cells bear respectively 

 black and the splashed white, blue can only be formed by the 

 heterozygous union of these two pure forms. The case further 

 illustrates the impossibility of basing expectation on analogy in 

 dealing with these phenomena (6). 



In Cats, Mice, Rabbits and Pigeons, the blue varieties are all 

 gametic types which can be fixed without difficulty. Ther is nothing 

 externally which would lead an observer to suppose that the blue 

 of a pigeon is more possible gametically than the blue of a fowl, yet 

 experiment shows that this is the fact. 



An inspection of the lists given above shows that it is practically 

 impossible to make any general statement as to which characters are 

 dominant and which are recessive. The principle expressed by de 

 Vries that the dominant character is phylogenetically older is no 

 doubt nearer the truth than the contrary statement would be, but it 

 is contradicted by not a few facts. For example the rose and pea 

 combs of fowls are evidently later in origin than the single comb. 

 Petalody of the Calyx, as C o r r e n s (38 ) remarks, can by no means 

 be regarded as an original form. Hornless cattle must surely have 

 been derived from horned progenitors. Other such illustrations are 

 seen in the case of colour-inheritance. For example the coloration 

 known in fowls as "Brown-breasted" is unquestionably of later origin 

 than the Bankiva colour of Brown Leghorn, over which it dominates 

 at all events in females (see Fig. 16). Black in pigeons is dominant 

 over the Blue Rock colour (Staples -Browne, unpublished). 



A generalisation may also be attempted on different lines. It 

 may be suggested that in the dominant type some element is present 

 which is absent in the recessive type. The difficulty in applying such 

 a generalisation lies in the fact that not very rarely characters do- 

 minate which appear to us to be negative. (For example. List I. 

 20 and 23. In Sweet Peas and other plants there are instances of 

 lighter colours being dominant over the more fully pigmented. Con- 

 sequently we are almost precluded from regarding dominance as 

 merely due to the presence of a factor which in absent from the 

 recessive form. Not impossibly we may have to regard such 



^) Probably the blue-grey which appears in Fi from the cross of black Angus 

 cow. X White Shorthorn bull is similarly a heterozygous character. 



