268 Edmund B. Wilson: 
against the view that the sex of dioecious organisms can be 
determined by external conditions, despite some results (e. g., those 
of Russow) that have seemed to give it support. It may be 
regarded as probable that if external conditions do affeet sex it 
is through the modification of a mechanism that pre-exists in 
the germ-cells. The true interpretation of such results as have 
been reached by Professor R. Hertwig, later by Kuschake- 
witsch (1910) on the influence of delayed fertilization upon the 
sex of frogs, “ not yet apparent; but they do not, I think, stand 
in any necessary contradiction to the cytological facts determined 
in other animals. 
Works cited.') 
Baehr, W.B. von: Die Oogenese bei einigen viviparen Aphiden und die 
Spermatogenese von Aphis saliceti. Arch. f. Zellforsch., III, 1, 2. 
Baltzer, F., 1909: Die Chromosomen von Strongylocentrotus lividus und 
Echinus microtuberculatus. Ibid., II, 4. 
Boveri, Th., 1909: Über Beziehungen des Chromatins zur Geschlechts- 
bestimmung. Sitzungsber. d. Phys.-med. Ges. Würzburg, 1908—1909. 
— 1909b: Über Geschlechtschromosomen bei Nematoden. Archiv für Zell- 
forschung, IV, 1. 
Buchner, P., 1909: Das accessorische Chromosom in Spermatogenese und 
Ovogenese der Orthoptera etc. Arch. f. Zellforsch., III, 3. 
Castle, W. E., 1909: A Mendelian View of Sex-heredity. Science, 
N483 1X XIX, 740. 
Correns, C., 1907: Die Bestimmung und Vererbung des Geschlechts. 
Berlin. Also in Arch. f. Rassen- u. Ges.-Biologie, IV, 6. 
Edwards, C.L., 1910: The Idiochromosomes in Ascaris megalocephala and 
Ascaris lumbrieoides. Arch. f. Zellforsch., V, 3. 
Footand Strobell, 1909: The Nucleoli in the Spermatocytes and Germinal 
Vesicles of Euchistus variolarius. Biol. Bull., XVI, 5. 
Goldschmidt, R., 1904: Der Chromidialapparat lebhaft funktionierender 
Gewebszellen. Zool. Jahrb., Anat. u. Ontog., XXI, 1. 
— 1910: Das Problem der Geschlechtsbestimmung. Die Umschau, XVI, 11. 
Gross, J., 1904: Die Spermatogenese von Syromastes marginatus. Zool. 
Jahrb., Anat. u. Ontog., XX. 
!) This list includes only the titles of works that are directly referred 
to in the text. Many of the more recent works that have confirmed and 
xetended the earlier results have necessarily been omitted. 
