32 GUNNAR DAHLBERG 



different species of Dasypos (armadillos) give birth to young from 

 one egg, and that the number of young, which arise from this single 

 egg, varies with the different species. On the whole, the number 

 is fairly constant, e. g. in Dasypos Novenbicatus 4 young from the egg; 

 in Dasypos hypridus usually 8, but sometimes more, even up to 12. 

 The capacity of giving birth to a number of young from one egg is 

 thus a hereditary feature in these animals. Therefore, from a general 

 biological point of view, there is no reason for denying (as Bonnevie 

 does) the possibility of the hereditary nature of twin-birth from one ovum. 

 This fact together with the facts previously stated considerably 

 strengthen the belief that the capacity of giving birth both to two-egg 

 and to one-egg twins is inherited even if the question of the mode 

 of the inheritance of twin-birth from several points of view is "far from 

 being solved. It is, of course, unnecessary to point out that exact 

 countings would be much more valuable than the more or less exact 

 data obtained by means of Weinberg's differentiation method; it is 

 equally clear, however, that the practical difficulties in the way of 

 obtaining such values are well-nigh unsurmountable. 



LITERATURE CITED. 



1. Ahlfeld, F. 1902. Wie stellt sich das Verhältniss der eineiigen Zwillinge zu 



den zweieiigen? Zeitsclirift f. Geburtshilfe u. Gynäkologie. Bd. 47, Heft 2. 



2. Haur, E., Fischer, F., Lenz, F. 1921. Grundriss der menschlichen Erblichkeits- 



lehre und Rassenhygiene. Bd. 1. München. 



3. Bonnevie, K. 1919. Om tvillingfödslers arvelighed. Norsk Mag. f. Laegev. i\:o 8. 



4. COBB, M. W. 1915. Evidence bearing on the origin of liunian twins. Science 



N. S. N:o 41, p. 501. 



5. Davenport, Ch. B. 1920. Influence of the male in the production of liuman 



twins. The American Natuiiist. Bd 54. 



6. Newman, H. 1917. The Biology of Twins. Chicago. 



7. Prinzing, F. 1907. Die örthlichen Verschiedenheiten der Zwillingshäufigkeit und 



deren Ursachen. Zeitschrift f. Geburtsh. u. Gynäk. Bd. 60, p. 420. 



8. HuMPE, K. 1891. ilber einige Unterscliiede zwischen eineiigen und zweieiigen 



Zwillingen. Zeitsclirift f. Geburtsh. u. Gynäk. 



9. Weinberg, W. 1902. Beiträge zur Physiologie und Pathologie der Mehrlingsge- 



burten beim Menschen. Pfliigers Archiv f. d. gesamt. Physiologie, Bd. 88. 



10. — 1903 a. Methode und Ergebnis der Erforschung der Ursachen der Mehr- 



lingsgcburten. Virchows Arch. 171, p. 340. 



11. — 1903 b. Neue Beiträge zur Lehre von den Zwillingen. Zeitschrift f. Geburtsh. 



u. Gynäk. Bd. 48, p. 94. 



12. — 1909! Die Anlage zur Mehrlingsgeburt beim Menschen und ihre Vererbung. 



Archiv f. Bässen- und Gesellschaftsbiologie. 



