On the Effect of Centrifugal Force on the Frog’s Egg. 393 
early cleavage. The same is true for the ovarian egg of the toad, fig. 3. 
With closely consecutive stages it is much more difficult to make quanti- 
tative comparisons. 
Biataszewicz found that the frog’s egg increased in volume pro- 
gressively after it was placed in water (except while the permteiline 
space was forming) and that this occured whether it were fertilized or not. 
ln this Connection might be mentioned the fact recorded by Backman 
and Rundström that the osmotic pressure of the frog’s egg drops from 
that of frog’s serum to that of pond water from the time it leaves the 
ovary to the first cleavage. This decrease in osmotic pressure is pro- 
bably due to absorption of water, although Backman and Rundström 
interpret it differently. This absorption of water, and the mixing of the 
Contents of the germinal vesicle vith the cytoplasm, accounts for the de- 
crease in viscosity of the egg after it leaves the ovary. 
Literature. 
Backman and Rundström, 1909. Physikalisch-chemische Faktoren bei der Embry- 
onalentwncklung. Biochem. Zeitschr. XXII, S. b90 
Biataszewicz, 1908. Beiträge zur Kenntnis der Wachstums Vorgänge bei Amphibien- 
embryonen. Bull, de l’Acad. des Sc. Cracovne, Math.-Nat., Okt. 
Gurwitsch, 1909. Über Prämissen und anstoßgebende Faktoren der Furchung und 
Zellvermehrung. Arch. Zellforschung, II, S. 495. 
Konopacka, 1908. Die Gestaltungsvorgänge der in verschiedenen Entuicklungs- 
stadien zentrifugierten Froschkeime. Bull, de l’Acad. des Sc. de Cracovie, 
Math.-Nat. Juli, S. 689. 
McClendon, 1909. Cytological and Chemical Studies of Centrifuged Frog’s Eggs. Arch. 
f. Entwicklungsmech. XXVII, S. 247. 
Chemical Studies on the Effects of Centrifugal Force on the Eggs of the Sea Urchin. 
Am. Joum. Phj^siol., XXIII, p. 460. 
■ On the Nucleo-albumin in the Yolk-platelets of the Frog’s Egg, with a Note on 
the Black Pigment. Ibid., XXV, p. 195. 
Morg.an, 1906. The Influence of a Strong Centrifugal Force on the Frog’s Egg. Arch. 
f. Entwicklungsmech. XXII. 
Rhumbler, 1900. Physikalische Analyse von Lebenserscheinungen der Zelle, III. 
Ibid. IX, S. 63. 
