254 CLAUDE W. MITCHELL 



SUMMARY 



1 . Continued low nutrition of the rotifer, Asplanchna amphora, 

 reduces male production to zero. 



2. Well-fed individuals, of the humped type, tend to give birth 

 to about 20 per cent of male producers. 



3. Dissolved metabolic products or other substances are not 

 significant factors in male production. 



4. Starvation of low potential females (produced by poorly 

 nourished mothers) results in non-male production. 



5. Starvation of high potential young females (produced by 

 well-nourished mothers) during the first five hours after birth, or 

 the growth period, results in copious male production. 



6. Starvation of high potential young females during the second 

 five hours after birth increases little, if at all, the amount of 

 male production. 



7. Maximum male production is determined by three factors, 

 physiological rhythm, high nutrition, and starvation during the 

 growth period. 



8. The first of these influences is one which extends through 

 a number of generations; the second works upon the generation 

 preceding the male producer; the third acts directly upon the 

 male producing generation itself. 



BIBLIOGRAPHY 



IssAKOWiTSCH, A. 1907 Geschlechtsbestimmende Ursachen bei den Daphniden. 

 Archiv. f. Mikr. Anat. u. Entw., Bd. 69, pp. 223-244. 



Mitchell, C. W. 1913 Experimentally induced transitions in the morpholog- 

 ical characters of Asplanchna amphora together with remarks on sex- 

 ual reproduction. Jour. Exp. Zool., vol. 15, pp. 91-130. 



« 



NussBAUM, M. 1897 Die Entstehung des Geschlechtes bei Hydatina senta. 

 Arch. f. Mikr. Anat. u. Entw., Bd. 49, pp. 227-308. 



Pap.a.nicolat;, G. 1910 tJber die Bedingungen der sexuellen ^Differenzierung 

 bei Daphniden. Biol. Centralb. Bd. 30, No. 13, pp. 430-440. 



Powers, J. H. 1912 A case of polymorphism in Asplanchna simulating a muta- 

 tion. The American Naturalist, vol. 46, pp. 441-462, and vol. 47, pp. 

 526-552. 



PuNNETT, R. C. 1906 Sex-determination in Hydatina with some remarks on 

 parthenogenesis. Proc. Roy. Soc. B., vol. 78, pp. 223-231. 



