320 The Oogenesis of the Tortoise 



Stage I. 



The Follicle. — From the very first, the appearance of the oocyte, differs 

 from the follicle cells in that the chromatin of the latter, at first very 

 similar to that of the young germinal vesicle, being in the form of dis- 

 tinct network of irregular grannies suspended in a clear nuclear matrix, 

 increases considerably and consequently stains more deeply. As the oocyte 

 grows, the nuclei of the follicle cells lose their spherical form, and be- 

 come more or less flattened, the elongation being in a plane vertical to 

 the egg surface. 



The young germinal vesicle preserves its spherical form. It seems to 

 grow rapidly — much more so, at this time, at least, than does the cyto- 

 plasm. At first, the ground substance of the germinal vesicle is clear, 

 showing the chromatin network beautifully. The increase in size seems 

 to be due to the increased amount of karyolymph. At first the chromatin 

 has the form of granules suspended in or attached to a network of 

 hyaline threads, but this lasts only for a brief period. The granules 

 increase rapidly and soon obscure the hyaline matrix and the nuclear 

 network. Consequently the young germinal vesicle stains more deeply 

 now. 



At first some of the granules imbedded in the linin network are 

 larger than. the rest; are more spherical; stain more deeply, and are 

 distributed about equally throughout the germinal vesicle (Plate VII, 

 Fig. 91; Plate I, Fig. 17). These spherical bodies become obscured as 

 the irregular granulation of the matrix becomes more marked. I sus- 

 pect that it is these larger spherical chromatin bodies that are more or 

 less directly responsible for the granules appearing around them. 



The Nucleoli. — The Avhole germinal vesicle being filled with granules, 

 till only traces of the original network can be seen, there appears at the 

 periphery one or two bodies larger than the former spherical chromatin 

 bodies, and having all the characteristics of true nucleoli. The principal 

 characteristics which serve to identify this as a nucleolus are : First, its 

 position, which is identical with that of all the subsequent nucleoli which 

 make their appearance ; and second, the appearance, within it, of vacuoles, 

 which cannot be seen in the spherical bodies of the network. As regards 

 size and shape, it is not especially distinguishable from the larger spheres 

 of the chromatin network. In its staining reaction, also, it resembles 

 those bodies. On account of its peripheral position, however, I entertain 

 considerable doubt as to its being one of those early spheres merely aug- 

 mented in size. 



The cytoplasm, also, at first becomes more and more turbid, and 



