Experimental Studies on Germinal Localization. 7 



During the 20-30 minutes following Its release the ripe, un- 

 fertilized egg becomes nearly spherical (and hence appears con- 

 siderably smaller In polar view), the membrane by which it is 

 at first surrounded separates more widely from the egg, finally 

 ruptures suddenly, and then quickly draws together at one side, 

 where It Is thrown off as a mass of debris attached to the egg 

 (Fig. 2).^ Following this, a substance which at first surrounds 

 the egg as a thin, transparent layer swells up to form a jelly, which 

 raises the egg slightly from the bottom. The wall of the ger- 

 minal vesicle breaks down at about this period (20-30 m.), leav- 

 ing a clearer space In which the first maturation-figure appears. 

 The white polar areas are still clearly visible, and the egg, still 

 unfertilized, now gives the appearance of being surrounded by a 

 very broad, horizontal pigment-ring, which, though often faint 

 and with vague boundary, is always distinctly visible (Figs. 3, 

 4). The ring recalls that described by Boverl ('01) in the egg 

 of Strongylocentrotiis , though relatively broader. The egg of 

 Dentaliiim thus shows a visible stratification of material analo- 

 gous to the zones seen In Strongylocentrotiis ; but, unlike the lat- 

 ter, the zones of Dentaliiim clearly pre-exist before even the pre- 

 paratory changes of maturation take place. 



Sections and total preparations of the flattened egg, fixed shortly 

 after Its discharge or removal from the ovary, show that a distinct 

 structural modification exists in each of the white areas, at this 

 period much more marked in case of the lower or vegetative area. 

 Surrounding the lower pole (Fig. 10) is a very distinct mass of 

 dense almost homogeneous protoplasm, of approximately the same 



1 All the figures were outlined as accurately as possible with the camera, and 

 with the exception of Figs. 10-13 and 33, 38-41, are enlarged to the same scale 

 (150 diameters). They are only schematized in that the pigment is represented 

 by stippling, whereas the color does not actually appear in the form of dis- 

 tinct granules, but as a nearly uniform hue. The stippling somewhat exag- 

 gerates the distinctness of the pigment as seen in most individuals; though in 

 the most deeply pigmented ones, viewed under strong direct light, the color 

 appears with great distinctness and its limits may be clearly seen. The opera- 

 tion of cutting usually leads to disturbances in the arrangement of the pig- 

 ment, so that frequently no definite color-pattern can be clearly made out in 

 the dwarf embryos. I have only represented the pigment in cases where its 

 boundaries could actually be seen. 



