324 The Oogenesis of the Tortoise 



egg should be important evidence of the persistence of the centrosome of 

 which it is a direct continuation. 



The cytocenter, notwithstanding its many peculiarities, often presents, 

 even in this second stage of the egg, when the cytoplasm has become very 

 granular, the principal features of a typical sphere, with a central granule 

 or granules, such as we find at the beginning of growth (Plate I, Fig. 33; 

 Plate II, Fig. 38; Plate III, Figs. 56, 65; Plate VII, Figs. 96, 97). 

 Furthermore, it often shows very distinctly the surrounding radiations 

 of the true aster (Plate I, Fig. 33; Plate II, Figs. 30, 33; Plate III, 

 Figs. 56, 60; Plate IV, Fig. 68). 



The central granule is not always visible. Its place may be occupied 

 by what seems to be a round hole or an unstained transparent body 

 (Plate II, Fig. 49, 51; Plate III, Fig. 65), or by an irregular network 

 (Plate III, Fig. 63; Plate V, Fig. 75; Plate VI, Figs. 78, 82). This 

 network-condition of the center is most frequent in the third stage of the 

 egg, when the yolk-bodies are being formed at the periphery. The net- 

 work often has a denser central portion (Plate VI, Figs. 81, 83; Plate 

 IV, Figs. 69, 71), in the center of which a deeply-staining body often 

 appears (Plate IV, Fig. 69; Plate VII, Fig. 84). Eadiating from this 

 dense central body, are numerous straight fibers passing through the 

 network out into the cytoplasm of the peripheral zone, suggesting most 

 certainly the original sphere with its radial fibers, etc. 



A form of the cytocenter, which is more common in the early stages 

 of the second period of growth, is that of a comparatively homogeneous, 

 slightly granular or fibrous mass, as seen in Plate I, Fig. 35 ; Plate II, 

 Figs. 37, 29, 45, etc. Slight or even pronounced differentiation of this 

 can in most cases be made out as in Plate IV, Fig. 67 ; Plate III, Figs. 

 55, 64. The more homogeneous ones of this kind are possibly caused 

 in part by the reagents, for they are occasionally contracted so as to 

 leave an open space extending partly around them (Plate I, Fig. 35; 

 Plate II, Fig. 39). But this does not appear in those represented in 

 Plate II, Figs. 37, 45. 



It is difficult to suggest any reason why the reagent should have such 

 effect in one case and not in others. The cytocenter assumes these 

 different forms in the same ovary, treated with the same reagents. Many 

 of the different forms can be seen on a single slide or on a series of 

 slides made from the same serial sections of a single ovary. 



While different stains differ in their power of rendering the fibers and 

 granules prominent, the variety of forms can by no means be attributed 

 to the effect of stains. 



Staining Effects. — The cytocenter is eminently cytoplasmic in its stain- 



