322 A. W. BELLAMY. 



* 



archenteron in the early gastrula stages, e.g., become pigmented 

 and most densely where cell division is most rapid. 1 And to 

 anticipate somewhat, the subjection of early gastrula stages to 

 strongly inhibiting conditions, results in a marked diminution of 

 pigment in the dorsal lip regions. 



The data further indicate that the polar axis as well as other 

 axes that arise later in development are primarily gradients in 

 fundamental physiological conditions or processes, which are 



FIG. i. Semi-diagrammatic view of a section through the germinal vesicle 

 and pedicle of a full grown ovarian egg. b.v., blood vessel in the theca; /, follicle 

 cells; g.v., germinal vesicle; p, pedicle; lh., theca. 



made evident in several ways, such as, the differential cleavage 

 rate which results in a gradient in cell size, by gradients in 

 susceptibility, etc. (see pp. 322-328). 



Discussion of the question of whether the location of the 

 pedicle and the localized blood supply is related in any way to 

 the definitive bilaterality remains for future consideration. 



The fact that the pedicle is equatorial in position is of course, 

 merely a necessary consequence of the way polarity and the 

 accompanying distribution of pigment is determined by the 



blood supply. 



IV. EXPERIMENTAL DATA. 



i. Susceptibility to Lethal Concentrations of External Agents. 

 The early stages of the frog egg are extremely resistant to 

 toxic agents. Eggs just beginning to segment, when placed 



1 King (1902). 



