INHERITANCE IN HYDATINA 89 



low viability was wholly ineffective. From this I judge that 

 inbreeding (and selection?) had produced a line homozygous 

 with respect to viability. 



The sex ratio (proportion of male-producing females) is inher- 

 ited. In two series of parthenogenetic lines, each hne of which 

 was produced by inbreeding from the preceding line, the sex 

 ratio remained nearly constant. In one series the ratio was about 

 35 per cent of male-producers, in the other series about 20 per 

 cent. The effect of crossing on the sex ratio is not clear, as the 

 labor of rearing several parthenogenetic lines prohibits the ac- 

 quiring of sufficient data. The experiments described in this 

 paper are in fair accord with the assumption that numerous fac- 

 tors, or genes, unite in producing the sex ratio. A possible 

 method of harmonizing this assumption with contradictory 

 results previously published is discussed above. 



BIBLIOGRAPHY 



Baltzer, F. 1910 tJber die Beziehungen zwischen dem Chromatin und der 

 Entwickelung und Vererbungsrichtung bei Echinodermenbastarden. 

 Arch. f. Zellforsch., Bd. 5, pp. 497-621. 



Jones, W. N. 1912 Species hybrids of Digitalis. Journ. Genet., vol. 2, no. 2, 

 June, pp. 71-78.' 



Pearl, R. 1910 Poultry notes. Maine Agl. Exp. Sta., Bull. 179, May. 



Shull, A. F. 1911 Studies in the life cycle of Hydatina senta. II. The role 

 of temperature, of the chemical composition of the medium, and of 

 internal factors upon the ratio of parthenogenetic to sexual forms. 

 Jour. Exp. Zool., vol. 10, no. 2, February, pp. 117-166. 

 1912 a III. Internal factors influencing the proportion of male-pro- 

 ducers. Ibid., vol. 12, no. 2, February, pp. 283-317. 

 1912 b The influence of inbreeding on vigor in Hydatina senta. Biol. 

 Bull., vol. 24, no. 1, December, pp. 1-13. 



ToYAMA, K. 1912 On certain characteristics of the silkworm which are appar- 

 ently non-Mendelian. Biol. Centralb., vol. 32, no. 10, October 20, 

 pp. 593-607. 



Whitney, D. D. 1912 Reinvigoration produced by cross fertilization in Hyda- 

 tina senta. Jour. Exp. Zool., .vol. 12, no. 3, April, pp. 337-362. 



