334 The Oogenesis of the Tortoise 



The evidences, so far produced by writers, of the disintegration and 

 disappearance of the centrosome are all of a negative rather than a 

 positive nature. Negative evidence of such a body as the tiny gran- 

 ule of the centrosome, or even of the surrounding microsomes and 

 radial fibers in the midst of a granular cytoplasm, may vs^ell create 

 doubt rather than conviction, to say the least. The few cases of mul- 

 tiple centrosomes, with which we have been, made familiar, were either 

 admittedly pathological, or else would seem to be temporary aggrega- 

 tions of the cytoreticulum having no connection whatever with a normal 

 centrosome. About all that can be said concerning pathological cen- 

 trosomes, if they be centrosomes at all, is that they are what they are 

 admitted to be, namely, pathological. Such evidence must be of doubt- 

 ful value in estimating normal structures. And when a few such ab- 

 normal structures are made the foundation of a whole system of beliefs, 

 as sometimes seems to be the case, what assurances have we that the 

 whole system is not as abnormal as the foundations on which it rests? 

 In the granular cytoplasm, like that of the egg, it is a comparatively 

 easy matter to find centrosomes almost anywhere, especially if one has 

 multiple centrosomes in the eye to begin with. Thus, in mounted sec- 

 tions of eggs like that represented in Plate VII, Fig. 87, a very regular 

 and pretty radial system of fibers surrounds those large yolk-bodies 

 that do not lie too closely packed for it to be seen. But who would say 

 that these yolk-bodies are centrosomes, or that such a system is homol- 

 ogous to a true aster or even comparable to the cytocenter as seen in 

 these eggs? 



The evidence of the continuity of the centrosome of the dividing 

 oogonia with that of the growing oocyte, is more satisfactory, it seems 

 to me, in this egg than in the egg of Limulus, and has tended to 

 strengthen my belief in the correctness of the views expressed in my 

 paper on that subject. 



That there is some constant relation between the cytoplasm and the 

 germinal vesicle, and that the latter is not merely a chemical mixture, 

 is suggested, first, by its constant position in the cytoplasm, its con- 

 stant relation to the cytocoel, and hence the cytocenter; second, by its 

 constant form, the persistence of the chromatin network, as well as 

 the peripheral arrangement of the nucleoli. I can find no evidence 

 that these nucleoli are influenced by gravity. No matter in what plane 

 the germinal vesicle is sectioned, the nucleoli are about equally dis- 

 tributed at its periphery. 



Chemical Processes. — One is almost forced to believe that the nu- 

 cleoplasm, which makes its appearance after caryokinesis of the oogonia 



