W. G. Van Name — Embryology of Etistylochus. 269 



Stricht, it is better to tear up the animals and to preserve the frag- 

 ments. In this way more rapid and complete penetration is possible. 

 The fragments of the animal with the eggs still in them were then 

 imbedded and sectioned in the manner described above. For these 

 early stages I found the picro-acetic fluid much the most satisfactory 

 fixing agent. 



For staining, Heidenhain's iron-haematoxylin method was usually 

 employed, but certain sti'uctures, such as the nuclear network of the 

 germinal vesicle, were shown much better by staining with Delatield's 

 haematoxylin. With these I generally used a ground stain of 

 Orange G or Bordeaux red, the latter proving the most satisfactory. 

 In using these, particularly the orange, care must be taken not to 

 stain too deeply, as the structure then becomes obscured, and it is 

 difficult or impracticable to extract the stain again. It apparently 

 makes no difference whether the sections are treated with the ground 

 stain before or after the haematoxylin. 



With saffranin, which was largely used by Van der Stricht, I had 

 little success. When the iron-haematoxylin method is used, the yolk 

 globules stain black, but usually a large proportion of them, or 

 sometimes all, become decolorized in the subsequent extraction with 

 the alum solution. If the extraction of the stain is only partial, 

 many of the yolk globules are left with a black center, because of 

 the tendency of the stain to dissolve away first on the outside of the 

 globule, where it is first reached by the solution. Such cases are 

 shown in Figs. 37, 38 and others. Such an object, especially when 

 close to the sperm-nucleus, may easily be mistaken for a centrosome 

 surrounded by a centrosphere. The absence of radiations and the 

 occiirrence of such objects in various points of the egg are usually 

 sufficient to show their true nature. 



The Germhial Vesicle. 



The shape of the eggs contained in the ovaries is determined by 

 the pressure of the adjacent eggs and tissues. With the exception 

 of those of advanced development — those which are forming or 

 have formed the first polar spindle — all contain a large round or 

 oval germinal vesicle (Fig. 1). In sections of fully developed 

 ovarian eggs this may be 0-02"'"' or more in diameter, and it always 

 contains a large nucleolus, which, as observed by Francotte and Van 

 der Stricht, in the early stages stains more deeply with haematoxylin 

 than in the later. It is nearly spherical and bounded by a definite 

 outline. At first it is homogeneous, in later stages sometimes vacuo- 

 lated, though this may be due to defective preservation. 



