520 



R. W. Hegner 



of the vesicular zone so that a figure has been introduced to show 

 the change in position of this structure (Fig. ii, g c. d). 



C.B. ^, e. A third layer makes its appearance if a fresh egg is 

 centrifuged for two hours. Before fixation this appears as a 



12. 



-khbl. 



^^^^^^^ V.Z. 



Fig. 10 Loagitudinal section through egg C.B. 4, d. 



Fig. II. Longitudinal section through the posterior end of egg CD. 4, d, showing the effects of a 

 centrifugal force applied for one hour upon the position of the pole-disc (gcd.). 



Fig. 12 Longitudinal section through the posterior end of egg C.B. 4, e, showing the effects of a 

 centrifugal force applied for two hours upon the position of the pole-disc. 



Fig. 13 Longitudinal section through the posterior end of egg C.B. 4, /, showing the effects of a 

 centrifugal applied for four hours upon the position of the pole-disc. gcd. = germ-cell determinants 

 (pole-disc), khbl. = "Keimhautblastem." n. = nucleus, p. = posterior, pt. = pathway made by 

 the outward movement of the pole-disc. v. = ventral, v.z. = vesicular zone. y. = yolk. 



Fig. 14 Trans%'erse section through egg C.B. 10, c. 



