314 The Oogenesis of the Tortoise 



the very earliest, including the oogonia. The smaller eggs are paler in 

 color, and they are distributed irregularly between the larger eggs, as 

 seen in Plate VII, Fig. 92. 



The ovary is covered with a thin membrane, evidently a fold of the 

 peritoneal membrane, and each egg is surrounded by two distinct coats 

 of membranous tissue, which are developed from the stroma of the germi- 

 nal mass. These latter membranes are richly supplied with blood- 

 vessels. 



The Germinal Mass. 



I have not traced the origin of the germinal layer in the embryo. 

 From the matured ovary, I infer that it develops in connection with the 

 peritoneal lining of the abdominal cavity, the original germ-cells becom- 

 ing surrounded by thin membranes apparently continuous with that 

 lining membrane. 



The germ-cells form a mass rather than an epithelium; and, in the 

 adult ovary, are divided up into distinct masses having more or less the 

 form of flattened oval ridges, slightly longer than broad, and distributed 

 between the larger eggs. It may be that this separation into ridges is 

 due to the growth of the eggs; and that, in the very young ovary, it 

 forms one continuous mass. 



The position of the smallest eggs in Plate VII, Fig. 92, indicates the 

 general arrangement of the germinal ridges, one ridge being usually 

 associated with each of the smaller eggs. There is represented in Plate I, 

 Fig. 1, a longitudinal section of such a germinal ridge; Plate I, Fig. 2, 

 a transverse section ; and Plate I, Fig. 3, a horizontal section of a germi- 

 nal ridge. 



The Oogonia. 



The germinal ridges consist chiefly of spherical cells, the oogonia, 

 each one being surrounded by a layer of cells, forming the stroma of 

 the ovary. Each of these stroma cells has a central flattened nucleus, 

 staining deeply, and all forming a circle around each oogonium, their 

 arrangement is such as to suggest a follicle; but the elongated and flat- 

 tened shape of these nuclei, as well as their closely packed chromatin 

 and consequently deep staining, renders them easily distinguishable from 

 the true follicle, which forms later within. It is this layer which evi- 

 dently forms the innermost tunic immediately surrounding the follicle 

 epithelium of the growing egg. 



The oogonia are spherical or slightly elongated. The nucleus is large 

 and spherical, and shows, at first, a very distinct network, apparently 

 imbedded in the hyaline karyolymph. The oogonia vary in size. In 



