322 The Oogenesis of the Tortoise 



cy. c.) ; and the sphere itself, because of its many peculiarities, not 

 usually recognized as belonging to the centrosome and sphere, I shall 

 call the cytocenter (Plate VII, Fig. 97, c. c. Fig. 85, c. c). I take this 

 cytocenter, in the larger eggs, to be the typical centrosome and sphere 

 of the earlier stages, modified by growth and by the deposit of yolk- 

 bodies and yolk-granules. 



I am very reluctant to introduce these names into an already over- 

 burdened vocabulary, but see no way of expressing myself without them. 



I have said that there are two rings of microsomes surrounding the 

 centrosome, forming the structural basis of the true attraction sphere 

 (Plate I, Pigs. 12, 13, 14, 15, 16, 17). That must be true in the very 

 early stages of development. In Fig. 17 is represented a young growing 

 egg more highly magnified. In Plate I, Fig. 13, is represented a section 

 through the attraction sphere at right angles to the egg-axis. But the 

 same appears to be true, also, of the oogonia (Plate I, Figs. 1, 2, 3, 4, 5, 

 and Plate VII, Figs. 93, 94, 95). The number of these circles seems to 

 increase as the egg grows (Plate VII, Figs. 96, 97; Plate II, Figs. 38, 

 50, 51; Plate III, Fig. 55). 



Stage II. 



The nucleolus, having first made its appearance in the preceding 

 stage, the number of these now increases rapidly. They correspond 

 roughly with the size of the germinal vesicle, increasing in number as it 

 grows. From a single nucleolus at the beginning, there may be a hun- 

 dred or more in the fully-grown germinal vesicle — a fact which has led 

 me to doubt their direct descent from the chromatin spheres of the first 

 stage. They vary considerably in the fully-grown germinal vessicle of 

 the third stage (Plate VII, Figs. 86, 87; Plate II, Figs. 30, 43, 63). 

 Their staining reaction is similar to that of chromatin. Hsematoxylin 

 and borax carmine make them conspicuous. The larger ones usually 

 show the central differentiation or vacuole common to most nucleoli. 

 It is rare, however, that they possess more than one of these (Plate III, 

 Fig. 63, 64, 65). 



The gei-viinal vesicle in this egg presents a somewhat remarkable uni- 

 formity as regards form. It is spherical, at times slightly oval, and 

 seems to retain this form from its beginning (Plate I, Figs. 11, 12, 18, 

 19; Plate II, Figs. 43, 44; Plate III, Fig. 62; Plate VI, Fig. 86?), and 

 even late into the final period of growth when the egg becomes filled with 

 yolk (Plate VI, Figs. 85, 86). 



Evidence of the nuclear reticulum is present throughout the three 

 stages, though the granular karyolymph renders the network indistinct. 



