333 The Oogenesis of the Tortoise 



part way around the nucleus. There is, outside of this, a thin layei 

 of cytoplasm. 



The fibrous nature of this cytoplasm is evident, especially in the 

 neighborhood of the centrosome, which is the focus of the astral system. 

 The astral system is a continuation of the cytoreticulum whose fibers 

 consist of microsomes apparently imbedded in a less stainable sub- 

 stance. The network is imbedded in a hyaline matrix, the cytolymph. 



This cytoplasmic structure is evidently continuous with a somewhat 

 similar structure in the nucleus. The bead-like stainable bodies em- 

 bedded in the linin network and which becomes aggregated into chro- 

 mosomes, are, so far as their relation to the nuclear reticulum is con- 

 cerned, similar to the cytomicrosomes. They differ, however, in their 

 staining capacity, as is well known in the case of other eggs also. 



Like the cytoreticulum, the nuclear reticulum is evidently suspended 

 or imbedded at first in a clear matrix or karyolymph. In both the cyto- 

 plasm and in the nucleus the matrix becomes turbid through the for- 

 mation of tiny granules. The deposit of these granules takes place in 

 the nucleus slightly earlier than in the cytoplasm, and seems to be 

 accompanied by the formation of nucleoli, just as in the cytoplasm it is 

 accompanied by the formation of yolk-nuclei, and considerably later by 

 the formation of true yolk-spheres. 



Evidence tending to show that these granules belong to the matrix 

 both of the germinal vesicle and of the cytoplasm, is afforded, in the 

 first place, by the fact that the nuclear reticulum can be seen even when 

 the egg is filled with yolk, and even so late as when the germinal 

 vesicle lies close under the egg-membrane (Plate VII, Fig. 87), and in 

 the second place, by such appearances as are represented in Plate V, 

 Figs, 72, 73, 74, and Plate VI, Fig. 81, where the granules have tem- 

 porarily accumulated in one spot, and have left the meshes clear behind 

 them. Here the fibrous cytoreticulum comes again prominently into 

 view. If this is due to a flowing movement in the interfilar substance, 

 it should afford evidence in favor of the reticular theory of protoplasm, 

 as contrasted with the alveolar. The fibrous structure of the cytoplasm 

 becomes again prominent, also, in connection with the cytocenter. 



I conclude that this reticulum, both of the nucleus and of the cyto- 

 plasm, is the real organized substance of the egg, and that, on the 

 other hand, the matrix with its contained granules possesses no organi- 

 zation, no permanent form, but is like any other chemical mixture of 

 organic substances, the culture medium, so to speak, of the organized 

 substance. 



