1918] ANIMAL PRODUCTION. 65 



The theory of the gene, T. H. Morgan (Amer. Nat., 51 {1911), No. 609, pp. 

 51S-5H. figs. 12).— In this paper the attempt is made to explain what the 

 genetic factor means to those who use it, and to answer some of the objections 

 to the factorial hypothesis of heredity. 



Statistical studies of the number of nipples in the mammals, J. A. Habbis 

 {Amer. Nat., 50 {1916), No. 599, pp. 696-70//).— A review of statistical studies 

 upon the type, variation, and correlation in number of mammse ; correlation 

 between the number of the young in the litter and the number of mammse in 

 the dam ; and inheritance of number and arrangement of nipples in swine. 



Observations on the skulls of hybrids between wild and domestic horses 

 and cattle, I. Philiptschenko {Compt. Rend. Soc. Biol. [Parisi, 78 {1915), 

 No. 18, pp. 636-638; abs. in Internat. Inst. Agr. [Rome's, Internat. Rev. Sci. and 

 Pract. Agr., 7 {1916), No. 2, pp. 246-248). — Measurements were made of skulls 

 of (1) hybrids between ordinary cattle and species of Bison, namely, American 

 bison {B. americamis) and " zubr " {B. bonasus) ; and (2) hybrids between 

 horses and zebras. The inheritance of skull characters in the case of these 

 hybrids showed the usual complexity found in hybrids between species. 



Studies on inbreeding'.— V 11, Some further considerations regarding the 

 measurement and numerical expression of degrees of kinship, R. Peabl 

 {Amer. Nat., 51 {1911), No. 609, pp. 545-559, fig. 1).—The author repeats and 

 extends his definitions of the basic concepts of inbreeding (E. S. R., 32, p. 665), 

 and on the basis of these definitions a new and more accurate method of meas- 

 uring and expressing numerically the degree of kinship between any two indi- 

 viduals whatsoever, whose pedigrees are known, is set forth and illustrated by 

 examples. A new constant, the partial inbreeding index, is described. Its 

 purpose is to indicate numerically the part of the total inbreeding exhibited in 

 the pedigree of any individual which is due to relationship between the sire 

 and the dam of that individual. 



Fecundity and the relation between male and female descendants in im- 

 proved German pigs, A. Machens {Berlin. Tierarstl. Wchnschr., 31 {1915), 

 No. 41, PP- 559-562; abs. in Internat. Inst. Agr. [Rome], Internat. Rev. Sci. and 

 Pract. Agr., 1 {1916), No. 2, pp. 256, 257).— The author studied 3,464 offspring 

 of the improved German pig recorded in the Herd-Book of the Breeders' Syndi- 

 cate of the Duchy of Brunswick. 



The average number of pigs per litter was found to be 9.56, the maximum 

 generally being reached in the fourth litter. The first litter of a young sow 

 usually contained more males than females. After the fifth litter the females 

 predominated. In small litters there was a majority of males, and in large 

 litters a majority of females. The fecundity was higher from September to 

 March than in the warm period during the rest of the year. 



Maturation of the ovum in swine, G. W. Cobnee {Anat. Rec, 13 {1911), No. 

 2, pp. 109-112). — The author gives a brief review of the literature of the sub- 

 ject, together with descriptive notes of a series consisting of 15 ova from 7 

 sows. 



The results of a study of these ova indicate that the sequence of maturation 

 is the same in swine as in previously studied forms of other orders. The first 

 polar body is extruded and the second polar division proceeds as far as spindle 

 formation before fertilization, the second polar body being cut off only after 

 the entrance of the spermatozoon. 



Experimental intersexuality and the sex problem, R. Goldschmidt {Amer. 

 Nat., 50 {1916), No. 600, pp. 105-118, figs. S).— A review of the quantitative 

 conception of sex determination. 



