490 



J. BRONTE GATENBY 



Now at a later stage of oogenesis as seen after non-osmicated 

 fixatives, the yolk-granules are observed to appear beneath or 

 within the wall of vacuoles, as shown in PI. 13, fig. 4, c. This 

 stage is drawn at a higher magnification in PI. 13, fig. 5 ; the 

 vacuoles are at v, and lie below the non-vacuolated clear outer 

 zone of the egg (oz) ; here and there on the trabeculae between 

 the vacuoles, but mainly beneath the vacuoles themselves, 

 are found in all stages of development yolk-spheres, ya, yb, yc. 

 Beneath this row of yolk-elements the egg-cytoplasm again 

 becomes non-vacuolated, forming a distinct inner zone at this 

 period iz. 



At a still later stage the inner zone free from yolk still persists, 

 but smaller in extent comparatively with the rest of the egg 

 (PI. 13, fig. 4, d). 



The individual yolk-granules may be noted to become formed 

 within certain of the clear vacuoles. In PI. 13, fig. 5, the vacuole 

 at ya contained a partially formed yolk-granule, or in other 

 words was filled intra vitam with yolk-substance so thin in 

 quality as not to be firmly coagulated by the fixative, and 

 thus gave the shrunken appearance noticed in ya and yb. 

 The yolk-sphere at yc was older and became fixed more 

 intensely, not undergoing shrinkage. 



I feel sure that many of the yolk-granules form by additions, 

 from the surrounding cytoplasm, to the fluid contents of the 

 vacuoles. The latter appear first, and then their contents 

 become richer and richer, till the yolk-granule is completely 

 formed. From the material available I was unable to say 

 whether the mitochondria take any part in yolk formation. 



13. Formation of Latebra. 



In PI. 13, fig. 4, are several stages in the formation of the 

 latebra ; in fig. 4, b, the oocyte cytoplasm presents a ring of 

 vacuoles which divide the egg into two parts, an outer (b) 

 and an inner (bl) ; the latter forms the main part of the 

 latebra. The latebra is that part of the inner region of the 

 egg where no coarse yolk-granules are ever formed. 



In PI. 13, fig. 4, c, a later stage is shown ; the yolk-granules 



