'GERM CELLS OF COELENTERATES 601 



are the cause of the type of variolation shown in figure 10, since 

 this characteristic group of vacuoles begins its formation at 

 about the place shown, and in these vacuoles deeply staining 

 granules are never found. There is, however, usually an inclu- 

 sion in the center of these small vacuoles. Certainly there is 

 not the distinct correlation between the liberation of nuclear 

 substances and the vacuolation of the cytoplasm which was 

 found in Campanularia. It is worthy of note that there are 

 no yolk spherules present in the cytoplasm of Aglantha at any 

 time, while in Campanularia yolk spheres were abundant and 

 were produced as the result of the liberation of substances from 

 the nucleus. 



As the egg grows it comes to be very markedly alveolar in 

 appearance as the figures in plate 2 show, and the vacuoles are 

 often very large. In these larger vacuoles of later growth stages 

 there are no inclusions, but in growing eggs which show such 

 inclusions there is clearly a rapid liquefaction and absorption 

 going on, hence their absence from mature eggs may merely 

 mean that the dissolving process has been completed and the 

 substances originally present in the granules have been absorbed 

 or else changed to a liquid which fills these spaces. 



Nucleus. The nucleus of oogonia is relatively very large, 

 occupying nearly the whole of the cell, displays no reticulum 

 or structural arrangement of any sort, but is filled with a close 

 packed mass of fine granules, and contains a very prominent 

 nucleolus. The structure, staining reactions and general appear- 

 ance of the nuclear contents are so similar to those of the cyto- 

 plasm that only with an immersion lens can a delicate nuclear 

 membrane be defined. The nucleolus appears to contain a 

 great deal of chromatin; perhaps most of that which is in the 

 nucleus is concentrated therein, but achromatic material is pres- 

 ent also; the nucleolus, therefore, has a mixed composition. In 

 most sections there is a clear space about the nucleolus, doubtless 

 due to shrinkage. Figure 2 represents a typical oogonium. 



In those cells which are clearly oocytes (fig. 7), i.e., in which 

 growth has begun, there is at first little difference in appearance 

 from the oogonia. The nucleolus is usually single, but occa- 



