438 MONTGOMERY. [Vol. XV. 



that a dense condensation of the fine granules of which they 

 are composed takes place. They continue to increase in size, 

 and gradually stain deeper as they do so, until they attain about 

 the dimensions given in Fig. 217 ; but I am unable to deter- 

 mine whether they all reach exactly these dimensions before 

 the metaphasic changes commence. At the conclusion of this 

 period of their development they are large bodies, regularly 

 spherical or oval in outline, and apparently without a limiting 

 membrane ; especially characteristic is their homogeneity and 

 their intense staining. 



Metaphasis. — These katabolic metamorphoses are intro- 

 duced when a few unstaining globules arise in the substance 

 of the yolk balls. These globules increase in number and size 

 until the yolk ball assumes a vacuolated appearance (Figs. 215, 

 217, 228). At the same time its ground substance loses its 

 staining power and no longer stains homogeneously. At the 

 commencement of these changes the yolk ball may even 

 increase somewhat in size, since the substance of the globules 

 is added to it. These changes continue until the yolk ball either 

 breaks up into the mature yolk globules {Yk. GL, Fig. 235), 

 or first breaks into a varying number of larger pieces, and then 

 each of the latter divides into yolk globules. The yolk globules 

 are usually nearly spherical in shape, and though by no means 

 equal in size are always larger than those of the other nemer- 

 teans examined. 



During the prophasis each yolk ball is enveloped by a clear, 

 structureless zone of cytoplasm ; but this surrounding zone is 

 usually not noticeable around the larger yolk-ball fragments, 

 and never around the mature yolk globules. 



As to the cause of the fragmentation of the yolk balls, I can 

 find no sure explanation from the facts at hand. However, the 

 appearance of the colorless fluid globules within their substance 

 must have an important connection with these katabolic changes, 

 since they characterize the commencement of this period of 

 change. It would seem likely that these colorless globules 

 represent a fluid constituent of the cytoplasm which has 

 actively or passively been taken into the yolk ball, — perhaps 

 from the clear cytoplasmic zone enveloping each yolk ball, — 



