The Development of Scyphomedusse. 239 



spindle, shows a later stage with all the chromosomes at the equa- 

 tor. The chromosomes are smaller and more numerous than in 

 figure 28, giving evidence that a splitting has taken place. In 

 fig. 28 there are about 9-10 chromosomes, in fig. 29, 18-20 and in 

 cleavage cells at least 18-20, so it appears that before the matura- 

 tion spindle has formed the conjugation of chromosomes has occur- 

 red. In the ovaries examined five eggs were found which showed 

 the first maturation spindle forming, but none showed the second 

 spindle and none the polar bodies. These facts, then, make it 

 clear that the polar bodies begin to form just before or at about 

 the time the eggs leave the ovary. In all probability this process 

 is completed and fertilization takes place while the eggs are in the 

 gastric cavity. 



A comparison of figures 28 and 29 with figures 27 shows how 

 small a portion of the germinal vesicle takes part in the forma- 

 tion of the chromosomes of the maturation spindle, a point already 

 noted in Coelenterates (Conklin 1908, Small wood 1909, G. T. 

 Hargitt 1909). What has become of the rest of the nuclear con- 

 tents? The chromatin in the maturation spindle (figs. 28, 29) is 

 manifestly less than that in the germinal vesicle (figs. 25, 27), and 

 no additional chromatin particles are found near the spindles. 

 Many eggs show spherical bodies in the cytoplasm close to the 

 nuclear membrane (fig. 25-27) sometimes with a vacuole about 

 them, and the question arises : is this chromatin which has migrated 

 from the nucleus before the rupture of the membrane? Such an 

 interpretation has been given to apparently similar bodies in 

 Hydromedusse eggs by C. W. Hargitt (1904 a, 1904 b, 1906) and 

 Smallwood (1909) . These extra-nuclear bodies of Aurelia stain as 

 intensely in the iron hematoxylin as do the chromosomes, but in 

 hematoxylin-eosin they take the red or acid dye. This is evidence 

 against their chromatic character, unles<* one assume that in the 

 cytoplasm they change their staining reaction, a not improbable 

 view. The conclusion must be reached that the greater part, at 

 least, of the achromatic substance and superfiu^as chromatin at 

 the time of the breaking of the membrane of the germinal vesicle 

 escape into the cytoplasm and are rapidly absorbed or mixed with 

 it. The relatively enormous size attained by the germinal vesicle 



