Oogenesis and Fertilization of (rrantia comjyressa. 'A79 



New Interpretations of the Nucleolar Extrusion in the 

 Oogenesis of Grantia cOxMPRessa. 



Dend}' (?) has described a peculiar process in the oogenesis of 

 Grantia, whereby pieces of the nucleolus are squeezed out into tlie 

 cytoplasm. In his figures 40—1:4 of Plate XXV Dendy has given 

 figures illustrating the process. 



I believe that such a peculiar occurrence is rare in the oogenesis 

 of animals, and for a time I had some doubt as to the correctness- 

 of the description previously given (J^). 



Further material has been collected and prepared by the best 

 new methods ; it is possible to confirm Dendy's previous description, 

 and to add new facts. The figures 3-10 of PI. V of this paper are 

 drawn from sponges fixed by Champy-KuU's method, and then 

 stained in Benda's alizarin and crystal violet. 



In PL V, fig. o, is drawn a choanocyte ; its nucleus stained 

 reddish brown, the nucleolus was violet, and the granules (G) in 

 the cytoplasm also stained a deep violet. I believe that some of 

 these granules, if not all, are to" be regarded as the mitochondria 

 of the cell. In certain cases the very large granules stained less 

 densely than the smaller ones, and these may be yolk (with dense 

 proteid content) or mitochondrial granules partly changed. 



In PI. V, fig. 4, is a collar cell just after it has begun to 

 metamorphose into an oogonium. This cell lay in the collar 

 epithelium, just beneath two normal choanocytes. The nucleolus 

 (plasmosome) has enlarged, and the nuclear network stained less 

 densely than that of most of the unchanged collar cells. Such 

 cells as the one drawn in PI. V, fig. 4, migrate from the flagellated 

 cavity into the mesoglea, where they undergo further remarkable 

 changes 



Figs. 5-10 are drawn from mesogleal oogonia; in fig. 5 the 

 nucleolus has increased enormously in size, while the cytoplasmic 

 granules derived directly from those already existing when the cell 

 was still a choanocyte are still evident, but often shrunken in size. 

 In subsequent stages the large plasmosome elongates and divides 

 by transverse fission, a large piece being shot out into the cyto- 

 plasm, as in PI. V, fig. 6, at N. In other cases large numbers of 

 plasm osomes collect inside the oogonial nucleus ; the latter seems 

 to collapse bodily and the contained granules pass into the 

 cytoplasm, as in PI. V, figs. 7 and 8. 



In a number of cases large pieces of the plasmosome are 

 separated from the central nucleolus, and pass to the nuclear 

 membrane; this becomes broken down, and the granules pass 

 through, as shown in PI. Y, fig. 10. 



In such stages a really extraordinary change comes over the 

 hitherto spherical nucleus. PI. V, fig. 8, shows an appearance 

 which is quite usual : here the nucleus has more or less become 



