360 EXPERIMENTAL STUDY OF INHERITANCE 



black forms (1,021 spotted, 345 black), i.e. in the Mendelian 

 proportion of 3 : 1 — a case of dominant-recessives inbred. 



Snails. — Lang paired " pure " five-banded forms of the 

 common or garden snail, Helix hortensis, with bandless forms 

 from bandless colonies. The young of the first generation were 

 all bandless, the banded character being recessive. When these 

 were paired the offspring were bandless and banded in the 

 Mendelian ratio, 3:1. Further experiments confirmed this, 

 not only as regards bands, but also as regards colour (yellow 

 or red), size, and the form of the umbilicus. It may be said, 

 therefore, that common snails [Helix hortensis and Helix nemoralis) 

 illustrate Mendelian inheritance. 



Poultry. — Numerous breeding experiments with poultry 

 have been made by Bateson, Bateson and Punnett, Hurst, 

 Davenport, and others, many of which show Mendelian pheno- 

 mena with great clearness, while others are strangely conflicting. 

 One of the reasons for the complicated results is evidently to be 

 found in the difficulty of securing thoroughly " pure " breeds, 

 for many that breed true as long as they are inbred tend to 

 liberate latent characters when the ordinary course of breeding 

 is departed from. 



Hurst contrasts the following characters, which usually show 

 themselves dominants and recessives ; but it has to be admitted 

 that the dominance — always complete f)r some characters — 

 is for others frequently, or even always incomplete — i.e. showing 

 traces of the corresponding recessives. 



Dominant Characters. Recessive Characters. 



Rose comb. Leaf comb, single comb. 



White plumage. Black plumage, buff plumage. 



Extra toes. Normal toes. 



Feathered shanks. Bare shanks. 



Crested head. Uncrested head. 



Brown eggs. White eggs. 



Broodiness. Non-broodiness. 



Davenport's copiously illustrated work is also of great interest. 

 He shows in case after case that the character dominant in the 



