No. 1, February, 1921] GENETICS 25 



like an ordinary chromosome, while the other behaves in the manner described for the un- 

 paired condition. Three cases of nondisjunction were observed. In two instances it was 

 a matter of the non-disjunction of the dyads of the supernumerary tetrad in the first matura- 

 tion division. The third is a "case of either maturational equational non-disjunction or a 

 peculiar type of reductional non-disjunction of the chromatids of the extra tetrad." — The 

 occurrence and behavior of the supernumeraries without non-disjunction make it possible to 

 have six kinds of spermatozoa; and should non-disjunction take place, two extra classes are 

 possible. Since non-disjunction occurs, it must duplicate a whole or a part of one of the 

 elements of a normal complex. It is obvious that the behavior of the supernumeraries must 

 influence the Mendelian ratios in any system of allelomorphs which may be carried by them, 

 since certain loci may exist in a double, treble, quadruple, or quintuple condition. These 

 various valences may be present in different germ cells of the same individual. — Mary T. 

 Harman. 



172. Castle, W. E. Whitman and Riddle on orthogenetic evolution in pigeons. Amer. 

 Nat. 54: 188-192. Mar.-Apr., 1920. — A critical but appreciative review of this monumental 

 work. Whitman believed his experiments to prove that Mendelism was relatively limited 

 in its application, but Castle shows that the results may be interpreted in conformity with 

 present Mendelian theory. — L. J. Cole. 



173. CoRRENS, C. Pathologie und Vererbung bei Pfianzen und einige Schliisse daraus 

 fiir die vergleichende Pathologie. [Pathology and inheritance in plants and a conclusion 

 derived therefrom for comparative pathology.] Mediz. Klinik. 16:354-359. April, 1920. 



174. CoRRENS, C. Eine gegliickte Verschiebung des Geschlechtsverhaltnisses. Botan- 

 ische Versuche zur Frage nach der Entstehung des Geschlechts. [A successful modification 

 of the sex-ratio. Botanical researches on the question of the origin of sex.] Natur u. Technik 

 2:65-71. 2 fig. 1920. 



175. Coulter, M. C. [Rev. of: Castle, W. E. Piebald rats and the theory of genes. 

 Proc. Nation. Acad. Sci. [U. S.] 5: 126-130. 1 fig. April, 1919.] [See Bot. Absts. 3, Entry 

 235.] Bot. Gaz. 70:326. Oct., 1920. 



176. Crozier, W. J. The intensity of assertive pairing in Chromodoris. Amer. Nat. 

 54: 182-184. 2 fi^. 1920. — This article is an additional note concerning a report published 

 by Crozier in Journal of Ex-perimental Zoology in 1918 [See Bot. Absts. 1, Entry 1472] in which 

 he shows that in the pairing of Chromodoris there is a "considerable degree of assortive con- 

 jugation with respect to size." In that report regression lines showing mean lengths of 

 mates pairing with individuals of a given length class were based on "artificial" measure- 

 ments; that is, the soft bodies were somewhat flattened and accordingly lengthened by the 

 process by which they were measured. In this report the relationship between the "artifi- 

 cial" and normal measurements of 74 individuals is established, and the regression plots 

 are revised in terms of the normal lengths. "The apparent intensity of homogamy in Chro- 

 modoris is but little affected, if anything perhaps slightly improved, by the reduction of the 

 original figures to the natural scale." — Sylvia L. Parker. 



177. Davenport, C. B. Heredity of twin births. Proc. Soc. Exp. Biol. Med. 17:75-77. 

 1920. — The incidence of twin births in the general population is about 1 per cent, but in cer- 

 tain families it rises to as high as 15 per cent, indicating that the tendency to twin produc- 

 tion is an hereditary trait. Only biovular twinning is considered in the present communi- 

 cation, and only such matings are selected for analysis as have produced at least two pairs of 

 twins. In such cases the immediate relatives — parents, brothers, and sisters, — are found to 

 produce twins from four to eight times as frequently as does the population at large. This 

 is about equally true for relatives on the father's side and on the mother's side, which shows 

 that the male exerts an influence on biovular twin production commensurate with that of the 

 female. In explanation of the nature of this influence of the male, it is pointed out that 



