66 INHERITANCE IN POULTRY. 



following evidence. First, of teratology. Extraneous paired papillae occa- 

 sionally occur on the sides of the single comb in pure-bred races. These are 

 known as ' ' side springs, ' ' and are considered by fanciers as grave ' ' defects. ' ' 

 Now such side springs are morphologically equivalent to the lateral ridges of 

 the pea comb. Second, there is the evidence of hybrid forms. Bateson and 

 Punnett (1905 a) show that when pea comb and rose comb are crossed the 

 second hybrid generation (F 2 ) gives single comb, as well as pea and rose combs. 

 This result may be interpreted as due to the fact that the gametes of a pea- 

 combed bird have either a tendency toward side- springs (= pea comb) or 

 they have no such tendency (= single comb) ; and the gametes of a rose- 

 comb bird have a tendency to produce two pairs of side combs (= rose comb) 

 or else they have no such tendency (= single comb). When two gametes 

 without the side-comb tendency come together in F 2 a single comb is pro- 

 duced. The necessity of assuming absence and presence of lateral combs 

 strengthens the view that the pea comb is made up of two elements median 

 and lateral. If median comb and side-springs are distinct elements, then 

 they should be independently inheritable. This result is realized on the one 

 hand in the single comb, and, I think, on the other hand, in the cup comb 

 (fig. 6), which consists of two side-springs without median comb. It is 

 realized also in the V comb of the Polish fowl, which is a cup comb of 

 which the anterior portion is typically not developed. 



That the V comb represents the posterior portion of a cup comb is supported 

 by the fact that it is not uncommon to find not one pair of papillae merely, 

 but two, three, or four pairs of papillae in Polish fowl and in second-genera- 

 tion hybrids. A row of three' or four papillae on each side of the head is a 

 close approach to a typical cup comb. 



The incompleteness of the cup comb where a V comb is produced may be 

 due to various causes. In the Polish fowl the upturned nasal process and 

 absence of a bony ridge over the nostrils appear to be the cause of the absence 

 of a comb there, and we have seen (p. 17) that the only undissociable char- 

 acteristics in the second- generation hybrids of Minorca and Polish are 

 those of high nostril and rudimentary comb. The second cause restricting 

 the development of the cup comb to its posterior limits is the presence of a 

 median comb anteriorly ; this is the case of the ordinary Y comb. The Y comb 

 is found in hybrids between single and V comb ; the anterior portion of the 

 comb is not suppressed here, because the bony roof of the culmen is com- 

 pletely developed, and the very presence of a large median comb there prevents 

 the development of the side-springs at the same niveau. In the development 

 of the comb of the hybrid there is, as it were, a struggle between the two 

 elements of median and lateral combs. The Y comb assumes a great variety 

 of forms, running the entire gamut from a single comb on the one hand to 

 (i) a cup comb or to (2) a pair of papillae on the other. I have already 

 (p. 10) referred to the variation of the length of the stem of the Y, series 



