POLYEMBRYONY AND THE DETERMINATION OF SEX. 319 



that, in all probability, the multiple twins of the armadillo jjroceed 

 from a single egg. 



The discovery of Marchal comes just at the right time to throw a 

 new light on this question, so interesting and so much discussed. 



From the fact that Encyrtus and Polygnotus which have issued 

 from the same larva are nearly always all males, or all females, it 

 is to be concluded that this is the one natural result of polyembrj^ony 

 and that the sexes will be separated in this manner whenever the 

 embryos jDroceed from the division of a single egg. 



The fundamental fact derived from this study is that all the 

 caterpillars, or larvae which contain a single chain of embryos, pro- 

 duce imagoes pertaining to a single sex. But as the same caterpillar 

 frequently supports two or three chains of embryos, there is nothing 

 astonishing in seeing males and females issue in more or less equal 

 numbers. Finally, the cases in which one finds individuals of both 

 sexes, but in unequal numbers, are explained by the partial abortion 

 of one of the chains and the survival of only a few individuals, 

 alongside of another normally developed chain. 



It appears that the discovery of polyembr3'ony confirms a fact 

 alread3^ suspected but incompletely demonstrated up to the present — - 

 that is, the knowledge that the determination of sex within the fer- 

 tilized ovum is definitely consummated before the first segmentation 

 of its nucleus. If, therefore, the facts taken from the observation 

 of the parasitic Hymenoptera apply equally to the higher aninuils, 

 it is inexact to speak, as is sometimes done, of an indilferent 

 embryonal period from the sexual point of view. The inditference 

 is probably apparent rather than real, and it appears probable that 

 once fecundation is effected the sex is irrevocably fixed. 



Walks cited. 



1879. Kleineuberg, N. : The development of the earthworm. Liimbricus tra- 

 pezoides Duges. Quart, jour. micr. sc, vol. 29, p. 200. 



1891. Bugniou, E. : Recherches sur le developpement postembryouairc. I'aiiato- 



mle et les moeurs de I'Euoyrtus fuseicollis. Reeueil zool. Suisse, T. V. 

 pp. 435-530, pi. xx-xxv. 



1892. Howard, L. O. : The biology of the Hymenopterous lusects of the family 



Chalcididje. Proc. V. S. Nat. Museum, vol. 14. pp. 567-588. 



1892. Driesch, H. : Entwickelungs-meehaiiisehe Studien. Exp. Yeriinderuugeu 



des Typus der Furchuug (Wirkuug von Wjirmezufuhr u. vou Druck). 

 Zeits. f. wiss. Zool, vol. 53, pp. 160-183. 



1893. Buguion, E. : Note sur la resistance de la Teigne du fusain aux basses 



temperatures de I'hiver. Bull. Soc. entom. Suisse, t. 8. 

 1893. Driesch, H. : Exogastrula u. Anenteria (Ueber die Wirkung von Warme- 

 zufuhr auf die Larveneutwickelung der Echiuiden). Mitth. der Zool, 

 Stat, zu Neapel, vol. 11, pp. 221-255, 



