No. 1, August, 1920] GENETICS 45 



344. Danforth, C. II. An hereditary complex in the domestic fowl. Genetics 4: 

 596. 5 fig. Nov., 1919. — Brachydactyly, syndactyly, and ptilopody (booting) are believed 

 by the author to be the somatic expression of a single gene and data in support of this view 

 are presented. — //. D. Goodale. 



345. Davenport, C. B. Influence of the male in the production of human twins. Aj 

 Nat. 54: 122-129. Mar.-Apr., 1920. — Both the fathers and the mothers of twins are found 

 to come from fraternities in which twins are about four times as frequent as in the population 

 at large. If only the data involving uniovular twins be considered, the frequency of twins 

 in the parental generation is twelve times that of the population at large, and is as high on 

 the father's side as on the mother's. Uniovular twinning is directly hereditary through eit her 

 parent as in the armadillo. It is tentatively suggested that biovular twinning is indicative 

 of marked reproductive vigor and relative absence of lethal factors on both sides. Since data 

 from comparative sources show that only a fraction of the eggs ovulated become fertilized 

 and reach late embryonic stages, and since there is good evidence that a high percentage of 

 originally twin pregnancies result in only a single viable foetus, the assumption seems justi- 

 fied that two-egg ovulations are relatively common in man, but that only a small part of such 

 ovulations actually result in twins that are born and recorded as such. — C. II. Danforlh. 



346. Dawson, Andrew Ignatius. Bacterial variations induced by changes in the com- 

 position of culture media. Jour. Bact. 4: 133-148. Mar., 1919. — As test organism author used 

 a long-cultivated strain of Bacterium colt. Preliminary test showed that maximum growth 

 of this organism on meat extract agar was attained in 9 to 11 days. In order to determine 

 effect on this organism of change in environment, so far as regards media, chemical analysis 

 was made of 9-days growth collected from 8 different media. These media consisted of 2 

 per cent agar to which was added various combinations of peptone, meat extract, edestin, 

 flour proteins, butter soap, glucose and glycerol. Varying proportions of these substances 

 were used, and in most cases no more than two appeared in each medium in addition to the 

 agar. One medium consisted of potato juice alone. Considerable variability occurred in 

 the proportions of nearly all bacterial constituents as the result of growth on these different 

 media. — Production of acid and gas in various carbohydrates was tested in litmus-carbohy- 

 drate-serum water after about 200 generations growth on each of the S different media. 

 Marked variability occurred; on one medium the organism behaved precisely as a B. coli- 

 communior, while on two others it possessed almost the type characteristics of a B. coli-com- 

 munis. — Agglutinability of organisms grown on all 8 media were tested with sera obtained by 

 injection into rabbits of bacteria grown on 4 of the media. Differences in agglutinability were 

 observed easily as great as those frequently utilized to demonstrate the existence of different 

 "strains" of the same basic organism. — Morphological changes accompanying growth on dif- 

 ferent media appeared to be relatively unimportant. [See Bot. Absts. 3, Entry 1237.]— 

 M. A. Barber. 



347. Dawson, J. A. An experimental study of an amicronucleate Oxytricha. I. Study 

 of the normal animal, with an account of cannibalism. Jour. Exp. Zool. 29: 473-513. 2 pi., 

 3 fig. Nov. 20, 1919. — Pedigreed cultures of Oxytricha hymenostoina carried 289 generations, 

 then from November 17, 1917, to April 30, 1918, in small petri-dish mass cultures, revealed the 

 absence of micronucleus during all phases of life-history of cultures. This amicronucleate 

 race apparently can live indefinitely under favorable environmental conditions without con- 

 jugation, autogamy, endomixis. In state resembling syngamy (a) animals fused in pairs die 

 or separate and reproduce with no signs of depression. (/>) cannibalism occurs causing in- 

 creased fission rate among progeny of cannibal for short time. [See also next following Entry, 

 348.]— Austin R. Middlcton. 



348. Dawson, J. A. An experimental study of an amicronucleate Oxytricha. II. The 

 formation of double animals or 'twins.' Jour. Exp. Zool. 30: 129-157. 1 pi., 13 fig. Jan 5, 

 1920. — Under conditions similar to those in which syngamy usually occurs is strong tendency 

 for formation of double animals, "twins," by plastogamic dorsal fusion. Twins have all 



