270 W. G. VanJSFame — Embryology of Eustylochus, 



Owing to the irregular shape of the eggs I cannot- say whether 

 the normal position of the germinal vesicle is central or eccentric, nor 

 whether the orientation of the egg is already determined. 



The germinal vesicle contains a more or less irregular network of 

 threads which do not stain very dark with Delafield's hfematoxylin, 

 although with the iron-hsematoxylin method they stain black. The 

 latter method is, however, poorly adapted for showing the real struc- 

 ture of this network and the early stages of the formation of the 

 chromosomes of the lirst polar spindle, on account of the tendency 

 to precipitate hematoxylin in excess in certain places, increasing 

 largely the apparent amount of chromatic substance and disguis- 

 ing the structure. This has also- been noticed by Francotte and 

 Klinckowstrom. Stained with Delafield's basmatoxylin the threads 

 are seen to form a network thickened at the nodes and where the 

 strands touch or unite with the nuclear membrane (Fig. 1). 



In immature ovarian eggs the cytoplasm is comparatively small in 

 amount and the germinal vesicle occupies a large proportion of the 

 bulk. The change in size and proportions which takes place as the 

 6gg ripens is due largely to the formation of the yolk, which, by the 

 time the ^^g is ready to leave the ovary, is distributed throughout 

 the whole of the cytoplasm in the form of small globules. This 

 comparatively uniform distribution of the yolk persists to a con- 

 siderable degree through all the maturation and early clea»'age 

 stages, so that as a rule only the space occupied by the mitotic 

 figures or nuclei, and sometimes their immediate vicinity, is entirely 

 free from yolk globules. 



The cytoplasm appears to consist of a delicate reticulum of threads 

 built up of microsomes staining dark blue with htiematoxylin, in the 

 meshes of which the yolk globules lie. Besides this there appears 

 to be a clear matrix in which both the reticulum and the yolk 

 globules are contained. Coe (1) observed this in the egg of Cere- 

 hratulus, but suggests that it may be an appearance due to the 

 shrinkage of the yolk spheres. If no such matrix exists it would 

 seem probable that the cytoplasm has really an alveolar rather than 

 a reticular structure. 



The Formation of the First Polar Spindle. 



The early stages in the formation of the chromosomes proceed 

 substantially as described by Van der Stricht (28). The observa- 

 tions of Francotte, including those on Prostheceraens, where 

 Klinckowstrom failed to find a spireme stage, are also much the 



