242 EDITH PINNEY 



masses of chromatin in the hybrid eggs show no more variabihty 

 in size than do those in the straight fertihzed eggs of Ctenohibrus. 

 They present no evidence of the ehmination of chromatin. One 

 hesitates, however, to draw any conclusions from such figures, 

 in view of the fact that the eggs differ shghtl}'^ in age and, fur- 

 ther, we have no real assurance that the relative size of these 

 masses mdicates the relative amounts of chromatin contained. 

 They are given here to show that the possibility of obtaining 

 evidence from this source was not overlooked. 



Giinther and Paula Hertwig considered that the lobed char- 

 acter of the nuclei in their Crenilabrus 9 X Gobius cf embryos 

 was a sign of nuclear degeneration. Figure 43 gives a series of 

 t\Tpical nuclei from the hybrid blastoderm, of which figure 26 is 

 a section. Nuclei from the slightly younger stage of a purely 

 bred embryo are shown in figure 44. The sunilarity obtaining 

 betw^een these, with regard to the lobed condition, militates 

 against the view that the lobes appearing in these older nuclei 

 are in any sense a sign of degeneration. 



The nuclei do, however, differ strikingly in one regard, and 

 that concerns the occurrence of nucleoli. There are typically 

 two jiucleoli present in the nuclei of the normal Ctenolabrus 

 blastoderms (fig. 45). The nuclei of the hybrid blastoderms 

 contain typically only one nucleolus. In the hybrid blastoderms 

 which show by their uniformity in cell and nuclear size that cell 

 division has been fairly normal, I have found but one exception 

 to this (fig. 43). Exceptions occur in those blastoderms in 

 which cell division has been very irregular. Such eggs show 

 great valuation in the size of both cells and nuclei, and abnormal 

 mitotic figures occur frequently- Variations in the occurrence 

 of nucleoli in these eggs is to be expected. Many of the nuclei 

 are very small and contain no nucleoli. A few nuclei show two 

 nucleoli and in one large nucleolus three nucleoli were found. 

 Even here single nucleoli are present in the majority of cells. 

 There is good reason to think that this difference in the hybrid 

 nuclei is due to the presence of the foreign chromatin. 



Moenkhaus, studyhig the nucleoli in his fish hybrids, found 

 that there were typically two present in each nucleus and he com- 



