Makch 22, 1907] 



SCIENCE 



465 



able to add many new and important facts to 

 those already known. The present work is, 

 however, to be looked upon rather as pre- 

 liminary — a first instalment of the extensive 

 experiments under way at Cold Spring Harbor. 



It would seem that studies dealing with 

 the hybridization of unit-characters relate 

 to the field of heredity rather than to that 

 of evolution. In fact, many evolutionists of 

 the old school deny the applicability of such 

 results to the theory of evolution. There 

 seems to be here a difference of opinion, 

 whether well founded or not the future will 

 decide. The opening paragraph of Professor 

 Davenport's paper leaves, however, no room 

 for doubt as to his attitude in the matter. 

 "Evolution proceeds by steps. These steps 

 are measured by the characters of organisms. 

 * * * Since the character is the unit of evolu- 

 tion it deserves careful study." 



The paper before us consists of thirteen 

 studies in hybridization with thirteen dif- 

 ferent races of fowls. The facts are presented 

 with admirable clearness and conciseness, 

 and despite the large number of details that 

 the subject demands the matter is handled in 

 a very attractive way. The seventeen plates 

 of photographs add materially to the interest 

 and importance of the work. 



For the detailed results of the author's ex- 

 periments, the original paper should be con- 

 sulted. It must suffice here to give a few of 

 the more salient points. 



When the single-comb, black Minorca is 

 crossed with the single comb black Polish 

 fowl " no characteristic [character ?] is in- 

 herited in strictly Mendelian fashion, for, in 

 no case is dominance complete." In the 

 second generation twenty-four individuals 

 were wholly black, and twenty-five wholly 

 black and white or mosaics. " I interpret this 

 irregular result to be due to the imperfect 

 dominance of black." 



When the single-comb, white Leghorn was 

 crossed with the Houdan, the offspring were 

 white with traces of black on one or more 

 feathers. When inbred, these hybrids pro- 

 duced 18 per cent, pigmented individuals like 

 the Houdan, — the Mendelian expectation be- 

 ing 25 per cent. — and the rest of the offspring 



was in part pure white and in part impure 

 white. The former proved to be all males 

 and the latter females! Other characters 

 also, nostrils, muff, beard, crest, polydactylism, 

 etc., show the influence of both parents in 

 the first generation, and incomplete dominance 

 and recession in the second, although a tend- 

 ency to separate into Mendelian groups may 

 be detected. 



In the next cross, Houdan by Minorca, 

 the author states : ' Striking is the nearly 

 universal imperfection of dominance.' Im- 

 perfect dominance is also recorded for many 

 characters of the five crosses that are next 

 described, but since the experiments were 

 carried only to the first generation, the results 

 are still too incomplete for satisfactory in- 

 terpretation. 



An interesting cross was made between the 

 Japanese Tosa fowl and the white Cochin 

 bantam; the former race is characterized by 

 abnormally long tail coverte. The first hy- 

 brids were like the Tosa fowl, although the 

 tail was intermediate; every feather of the 

 male was barred with white and in the female 

 the shafting was broadened. In the second 

 generation 28.1 per cent, were white to 

 71.9 per cent, pigmented individuals, but of 

 the sixteen white individuals only five were 

 without reddish pigment. " The forty-one 

 pigmented individuals show a curiously mixed 

 lot of coloration." One showed a Partridge 

 Cochin plumage which must have ' lain latent 

 in the white Cochin.' It is important to no- 

 tice that in this cross white is not dominant 

 in the first generation as with most other 

 races of fowls. 



The following four crosses were carried 

 through the first generation only. They show, 

 nevertheless, the complete dominance of 

 frizzling; the incomplete dominance of the 

 white of the white Leghorn over red of the 

 game; the complete dominance of long tail 

 over rumplessness (although one chick had no 

 tail!); incomplete dominance of the black of 

 the Cochin bantam over the red of the game. 



A clear and able summary and discussion 

 follows the detailed account of the experi- 

 ments. Unit characters are not regarded aa 

 rigid or immutable from the evidences of 



