228 CORA J. BECKWITH 



6. Chromosomes and continuity 



My results contribute little to the solution of this question, but 

 since some evidence in its favor appears in the nucleus of Hydrac- 

 tinia eggs, it can hardly be passed by without comment. As 

 previously stated, when the chromatin becomes diffuse, the net- 

 like arrangement of the chromatin is lost. This is brought about 

 by the threads becoming gradually arranged in groups of two 

 either parallel or cross-like threads (figs. 25, 26). These crosses 

 or parallel threads gradually fade out completely, leaving the 

 characteristic lightly staining nucleus (figs. 21, 27, 28). That 

 the chromosomes reappear in exactly the same way in which they 

 disappear, that is, as X's and parallel threads, is evident by com- 

 paring the figures just described with those of reappearing chro- 

 mosomes (figs. 29, 1, 30, 31). In fact, they are so exactly alike 

 in form, in many cases, that whether they are disappearing or 

 reappearing can only be decided by other conditions in the egg 

 and nucleus. It is hard to resist the impression that this identity 

 in their method of disappearance and reappearance is significant 

 of some sort of continuity. 



B. EUDENDRIUM RAMOSUM 



Maturation and fertilization 



The complete history of the chromatin in the maturation of 

 Eudendrium has not been worked out, but such stages as I have 

 establish its regular character. Maturation, fertilization and 

 development of the egg up to the planula stage take place in the 

 gonophore. The position of the nucleus after it leaves the center 

 of the egg differs from most other hydroids, since it does not lie 

 at the free surface of the egg as it ordinarily does, but at the inner 

 end which leads to the cavity of the gonophore (fig. 51). The 

 maturation and fertilization stages take place at this point. I 

 have sections only of material fixed in sublimate-acetic killing 

 fluid, so that there is always present in the resting nucleus the 

 heavy net-like structure caused by this fixation. 



