238 



The Journal of Heredity 



as 113.3, and from more recent data 

 Pearl"^ found the ratio to be 100.12. 

 This last figure coincides more nearly 

 with data collected by Gowen, giving a 

 ratio of 101.58. King^ found the 

 sex ratio of rats at birth to be 104.6. 

 Little has calculated the ratio in 

 mice to be 103.1, while Weldon's 

 material* gives a ratio of 104.1. The 

 ratio in man was found to be 105 by 

 Pearl and Salaman.^ Unfortunately, 

 there is no published data on the 

 sex ratio at birth of cats, so that 

 a comparison with the fetal ratio is 

 impossible. We are therefore unable 

 to tell whether there is a differential 

 intra-uterine mortality between the 

 sexes or not. 



White coat color in cats has been 

 recognized for some time past as a prob- 

 able Mendelian dominant representing 

 an extreme form of spotting. Little^** 

 has found a possibly similar case 

 in mice. Here a factor with somewhat 

 the same function behaves as a lethal 

 when present in the duplex condition. 

 To attempt to test this hypothesis for 

 cats, the litters of white, or nearly 

 white cats have been compared with 

 those of non-white females. The cats 

 classified as "nearly white" showed 

 at most an area of color not larger 

 than ten per cent of the entire coat. 

 Since white, or nearly white cats, 

 are not common, the chance of ob- 

 taining pregnant females was not great. 

 Twenty-five were, however, obtained 

 in the course of the experiment, 

 with a total of 102 fetuses. The 

 mean litter size of white females was 

 4.08 + 0.13, while that of non-whites 

 was 4.48 + 0.07. The difference is 

 0.39 ±0.15, which is 2.71 times its 

 probable error. This, of course, is not 

 a significant difference and can only 

 be regarded as an indication of a pos- 

 sible diminution in the size of white 



litters which might have become ap- 

 parent in the event of larger numbers. 

 If this is due, as in the case of the mice, 

 to the degeneration of the fetuses in 

 utero, a larger number of degenerating 

 fetuses should be found in the uteri 

 of white females than in non-white. 

 The records of degenerating embryos 

 found have been kept, and show that 

 out of 102 fetuses of white females, 11, 

 of 10.78 + 2.07 per cent were degene- 

 rating. In the non-white females, out of 

 55 1 fetuses, 25, or 4 . 54 + . 60 per cent 

 were degenerating. The difference is 

 6.25 + 2.16, which is 2.89 times the 

 probable error. The figures for the 

 non-white fetuses include one litter 

 composed of four degenerating fetuses 

 in utero, while attached to the ventral 

 body wall was a teratoma-like struc- 

 ture inclosing a fetus which had ap- 

 parently fully developed, and showed 

 at that time the skeletal structure and 

 hair formation of a full-term embryo. 

 This case has been considered abnormal 

 and pathological, and a recalculation of 

 the number of degenerating embryos 

 in non-white litters has been made on 

 this basis. With this correction, there 

 are 21 degenerating out of 547 fetuses, 

 the percentage being 3 . 84 + . 58. The 

 difference between whites and non- 

 whites then becomes 6.845 + 2.149, 

 which is 3.2 times the probable error, 

 which may be considered as a signifi- 

 cant difference, although the percent- 

 ages are so small that it is difficult to 

 be sure of the significance of such a 

 difference. Thus, the conclusion is 

 probably warranted that a significantly 

 greater number of degenerating fe- 

 tuses are found in white than in non- 

 white female cats. 



From the nature of the material used 

 it was impossible to know the sire of 

 any litter, but, as has been stated 

 before, the proportion of white cats 



« Pearl, R. The Control of the Se.\-Ratio. Maine Agric. Exp. Sta. Bull. No. 261. Part 3. 1917. 

 ^ King, H. D. and J. M. Stotensburg, (1915). On the Normal Sex Ratio and the Size of the 



Litter in the Albino Rat. Anat. Rec. IX. 

 * Weldon, W. F. R. Mice Breeding Experiments. Records of Matings. BiometrikaXl. 1916. 

 » Pearl, R. and R. N. Salaman. The Relative Time of Fertilization of the Ovum and the Sex 



Ratio Amongst Jews. Maine Agric. Exp. Sta. papers from the Biological 



Laboratory, No. 48, Vol. II. 1913. 

 10 Little, C. C. Note on the Occurence of a Probable Sex-linked Lethal Factor in Mammals. 

 Am. Nat. LIV, 1920. 



