870 



SCIENCE 



[N. S. Vol. XXXII. No. 833 



litter. From yellowX non-yellow matings, 

 325 litters have been obtained, includ- 

 ing 1,812 young, an average of 5.57 young 

 to a litter. These averages are considerably 

 higher than Cuenot's, indicating either a 

 healthier stock of animals or better experi- 

 mental conditions. Qualitatively, however, 

 the results obtained in the two cases are com- 

 pletely in accord. The yellow X non-yellow 

 matings produced larger litters than the yel- 

 low X yellow matings, but not so much larger 

 as we should expect if homozygous yellow 

 zygotes simply perished without otherwise af- 

 fecting the character of the litter. For, in 

 that ease, the two categories of litters should 

 be to each other in average size as 3:4, but 

 we find that they were really as 3.38:4. The 

 litters of yellow X yellow parents, instead of 

 being 25 per cent, smaller, are only 15.5 per 

 cent, smaller than those of yellow X non-yel- 

 low parents. In other words, when 100 pure 

 yellow zygotes perish, they cause 38 other zy- 

 gotes to develop in their stead. How can this 

 be brought about? Cuenot supposes that some 

 of the potential pure yellow combinations 

 really become heterozygous yellow combina- 

 tions and so swell the size of the litter. But 

 in that case the total percentage of yellows 

 should exceed 66.66 per cent., which it does 

 not in our experience. We are forced, there- 

 fore, to conclude that the perishing of a pure 

 yellow zygote makes possible the development 

 of a certain number of other fertilized eggs. 

 Two ways may be suggested in which this 

 might come about. First, more eggs may 

 normally be liberated at an ovulation than 

 there are j'oung born subsequently. In that 

 case, failure of some eggs to become attached 

 to the uterus may make the chances greater 

 that the remainder will become attached, or 

 the perishing of some may make the chances 

 greater that the rest will successfully com- 

 plete their development. Or secondly, the 

 production of a relatively small number of 

 young at one birth may lead indirectly to 

 more free ovulation subsequently, and so to 

 the production of a larger litter at a second 

 birth. It should be possible to test the valid- 

 ity of both these hypotheses experimentally. 



The result here described for yellow mice, 

 in common with that of Baur in the case of 

 Antirrhinum, would seem to show that a Men- 

 delian class may be formed and afterwards be 

 lost by failure to develop. In other words, a 

 physiological inability to develop may perma- 

 nently modify a Mendelian ratio, causing the 

 loss of an entire class. 



As regards the matter of selective fertiliza- 

 tion of the egg discussed by Wilson and Mor- 

 gan in connection with this case, it is evident 

 that nothing of the sort here occurs. 



PAPERS CITED 



Baieson, W., 1909. " Mendel's Principles of 



Heredity." See p. 119. 

 Baub, E., 1907. " Untersuchungen fiber die Erb- 



liohkeitsverhaltnisse einer nur in Bastardform 



lebensfahigen Sippe von Antirrliinmn majus." 



Ber. d. Deutsch Bot. Gesellschaft, 25, p. 442. 

 Cu£not, L., 1905. " Les races pures et leurs 



combinaisons chez les souris." Arch. Zool. Exp. 



(4), III., Notes et Revue, p. cxxiii. 

 1908. " Sur quelques anomalies apparentes 



des proportions MendeliSnnes." lb., IX. Notes 



et Revue, p. vii. 

 JOHANNSEN, W., 1909. " Elemente der exakten 



Erblichkeitslehre." Jena. 

 MOBGAN, T. H., 1905. " The Assumed Purity of 



the Germ-cells in Mendelian Results." Science, 



22, p. 877. 

 Wilson, E. B., 1906. " Mendelian Inheritance and 



the Purity of the Gametes." Science, 23, p. 



112. 



W. E. Castle 

 C. C. Little 



BussET Institution 



Haevaed Univebsitt 



FURTHER data REGARDING THE SEX-LIMITED IN- 

 HERITANCE OF THE BARRED COLOR PATTERN 

 IN poultry' 



In two previous papers^ the writers have de- 



' Papers from the Biological Laboratory of the 

 Maine Agricultural Experiment Station, No. 22. 



' Pearl, R., and Surface, F. M., '• On the In- 

 heritance of the Barred Color Pattern in Poultry," 

 Arch. f. Entmcklungsmech., Bd. XXX., pp. 45-61, 

 1910 (Roux Festschrift). "Studies on Hybrid 

 Poultry," Ann. Rept. Me. Agr. Expt. Stat., 1910, 

 pp. 84-116. 



