The Development of Scyphomedusse. 233 



stances an apparently more liquid substance, containing few yolk 

 spherules, in the center of the egg. This he believes is the ''pre- 

 cursor of the cleavage cavity." There was no evidence of such a 

 substance in Cyanea eggs, but in Aurelia the center of the egg in 

 a few cases showed what appeared to be a similar differentiation. 

 It is also clear that in both Cyanea and Aurelia a liquid substance 

 is present in the early cleavage cavity. It may be rather doubtful 

 whether this comes from a substance already differentiated in the 

 unfertilized egg, surely not in all cases. 



In eggs of most animals the second division is meridonal and 

 other workers have generally described the same thing in the Scy- 

 phomedusse. So it was found in Cyanea (figs. 6, 11) that such 

 might be the case. In view of the variations in the first cleavage it 

 was not surprising to find instances (figs. 4, 13) where the second 

 cleavage was equatorial, and this was not rare. This condition, 

 of course, is often found in eggs which are erratic and irregular 

 in cleavage as some of the Hydromedusse, Pennaria in particular. 

 It was possible to follow the cleavage in the living Aurelia egg 

 and to observe that in some cases the second division was. equator- 

 ial. When the first cleavage in Cyanea had been unequal a very 

 common sequence was for the large blastomere to divide before 

 the smaller giving a three-cell stage (fig. 5), a condition earlier 

 noted in Cotylorhiza (Goette 1887) and Aurelia (Hyde 1894). 

 The three cells were bf approximately equal size and thereafter 

 the cleavage was fairly regular. 



After the second division, cleavage is more or less regular, but 

 the cells are usually unequal in size. There appears to be no 

 very definite sequence of division, so far as could be determined, 

 nor was there any marked synchronism, since there were found 

 3, 5, 7, 8, 10, 12, etc., cell stages, as Hyde earlier noticed. The 

 impression obtained from the study of many eggs was rather that 

 of a certain independence of each blastomere in its division. In 

 the 8-cell stage (figs. 7, 14) the cleavage cavity, which first appeared 

 in the 2-cell stage (fig. 12) was larger, and this increase in size 

 continued through the later stages until in the blastula there was 

 a large cavity surrounded by a single layer of cells which were 

 smaller at one pole (figs. 10, 16). The cells were often so crowded 



