hargitt: pennaria tiarella and tubularia crocea. 181 



Before much growth has taken place, the spireme undergoes a 

 further change, the chromatin thread taking on the form of a number 

 of loops (Figs. 31, 32, 33), which, from the first, have a definite polar 

 arrangement; the attached portion of the loops being apparently 

 fastened to the nuclear membrane near a common point, the opposite 

 ends being always closely approximated to the opposite wall of the 

 nuclear membrane, though never attached to it. It is not always 

 possible, however, to demonstrate this condition, since the loops are 

 often long, and extend more than half way around the inner surface 

 of the nucleus. When a number of them cross one another there 

 results such a complicated figure that the polar arrangement, if it 

 exists, is entirely masked, the nucleus apparently containing a long 

 complex spireme. There is little doubt that such a polar arrangement 

 regularly constitutes a stage in the oogenesis of Tubularia crocea. 

 This seems to correspond to the synapsis found in so many other 

 animals, and described by several authors for coelenterates. None of 

 these authors, however, mentions the polar arrangement of the spireme. 

 I could not determine definitely the number of loops present, though 

 in the few that could be counted there seemed to be from nine to eleven. 



The further changes of this spireme can be determined only in part. 

 The polar arrangement seems to be lost after a short time and does 

 not appear again during the oogenesis, so far as I could find. Some 

 preparations (Figs. 34, 38) seem to give evidence of a splitting or 

 doubling of the threads composing the loops, but as this appearance 

 has been clearly seen in only a few cases, it may be purely accidental. 

 It would be difficult to conceive that a split condition was represented 

 in Figure 37, which shows a stage of about the same age as that of 

 Figure 38. The spireme continues to get finer and more delicate and 

 also more complex in arrangement, the thread taking on a granular 

 appearance, as shown in Figures 34 and 38. This change to a granular 

 condition continues to such an extent that, in the nearly mature egg, 

 the germinative vesicle shows, besides a nucleolus, only a mass of 

 granules arranged in a very extensive though delicate reticulum, 

 extending throughout the nucleus (Figs. 39-46). As the reticulum 

 is colored by plasma stains more intensely than by nuclear dyes, there 

 results the appearance so characteristic of the germinative vesicle of 

 Coelenterata and some other groups, in which the chromatin is very 

 finely divided and diffused. That the chromatin is present in the 

 reticulum and not in the nucleolus, will be made clear in the following 

 description of the changes which the nucleolus undergoes. This 

 extreme diffusion of chromatin is not always equally marked in differ- 



