H. HOUWI.NK. — EXPERIENCES PRATIQUEES DANS LES RACES DE VOLAILLES. 555 



frost bitlen, and often Ihe birds succomh. The resiill is llial ail hardy breeds 

 of fowls hâve small combs. 



The questions arises, whellier Ihe rigourous winlers ol' Ibilland are liie 

 cause of Ihe variations so often observed in pure breeds;' 



As the resuit of more Ihan 12" of frost, the combs, wallles, and toes may 

 be frozen, and if the bird does not succomb, its constitution and reproductive 

 System are considerably alïected. Is it possible that thèse influences may pro- 

 duce an efl'ect in future générations and give rise to variations and mutations? 

 Thèse questions the aulhor bas attempted lo invesligate systemalically. 



E.rperimenig willi rei^pevl to changes in form. — The results of thèse cxperi- 

 ments point to the conclusion tliat natural causes give rise to latent modifica- 

 tions in the normal bird; thèse may not manifest Ihemselves until the second 

 or laler générations, when new and abnormal forms may be produced'. 



Erperimenl^ in crossing aucIi new fonns witli llie normal Igjies. — As the 

 resuit of crossing such modified forms with the normal type, the majority of 

 the variations disappeared, and about 90 % normal Ijirds were obtained. An 

 analogous cross in the second génération gave rise to normal birds only. 



T/ie 7-c!>i/ll of ciintinued sélection. — • By continued sélection of the modified 

 forms, there resullf-d variations of greater importance: with, incidentally, a 

 return lo the normal form. Among the modified forms occurred some fixed 

 types which reseml)led exactly certain kTlo^\n races, sucli as the Bralianconne, 

 and the Caumont breeds. 



The aulhor deduces from bis experiments that Ihose latent characters due 

 to natural causes are not inheriled in anv regular manner, but are inconstant 

 and unfixed; thèse be calls intermediate rariatinns. 



By continued sélection thèse variations may be rendered fixed and stable: 

 thèse be calls /?««/ variations. 



The conclusion reached by the aulhor is as follows : 



(A) Natural sélection produces tluctuating variations in races of hardy 

 fowls' . 



(B) By continued breeding of tiiese lluclualing varieties, produced by 

 natural sélection, new fixed races may be formed-. 



(Cj In agreement wilh Darwin's theory, the formation of races may be 

 explained not only by mutations, but also by lluclualing variations, produced 

 by natural sélection. 



1. Non geni'tic fiiclors. 



2 l'.iimljiiialioiis of lum genetic and genetic factors. See experimonls 10!0-l'.)l". 



