MorpPHoLoGy oF DEVELOPMENT 21 
equatorial plane of the cell during the spindle stage. In plants 
these materials consist of cellulose which hardens and forms a 
membrane separating the two cells. In animals they consist 
of a different substance which possibly forms soaps (Quincke’s 
albumin soap?) at the surface of the egg. These substances 
(soaps ?) induce streaming phenomena, which according to the 
writer lead to the division of the egg into two spheres.! 
Fig. 12 Fig. 13 
Fics. 12 and 13.—The first cell division completed. 
T. B. Robertson has lately brought forward a pretty demon- 
stration of this view.” If a drop of olive oil is placed on the 
surface of water and upon one diameter of the drop there is laid 
a thread which has been previously moistened with an alkaline 
fluid (e.g. N/10 NaOH), the drop divides into two drops, just 
like the sea-urchin egg in the previously described figures. By 
suitably varying the viscosity of the oil and other conditions 
one can reproduce all the phases of cell division which can be 
observed at cleavage during the separation of the ceils. The 
alkali on the thread forms a soap with the oleic acid, and this 
soap induces streaming phenomena which lead to the splitting 
of the drop into two.* In discussing the possibility of a synthe- 
1 Loeb, Archiv f. Entwicklungsmechanik, I, 468-70, 1896; XXVII, 138, 1909; 
Biitschli, zbid., X, 52, 1900. 
2T. B. Robertson, Archiv f. Entwicklungsmechanik, X XVII, 29, 1909. 
3 Loeb, The Dynamics of Living Matter, New York, 1906, pp. 55-58. 
