398 



ANN BISHOP 



period after fission than usual, A similar phenomenon was 

 observed by Johnson (13) during his study of the Stentors. 



Stein (28) describes cases where the meganucleus was only 

 a quarter of the body length, was not lobated, and lay in the 

 anterior end of the body. These were, I 'feel certain, also stages 

 in fission. 



The meganucleus is surrounded by a nuclear membrane 

 which adheres firmly to the nucleoplasm. It is best shown 

 in individuals which have been fixed and stained in methyl 

 green and acetic, especially if the cytoplasm has been teased 

 out prior to fixation. 



In preparations well fixed and stained with iron haema- 

 toxylin the internal structure of the meganucleus is plainly 

 visible. It consists of numerous granules, which stain deeply 

 with iron haematoxylin, embedded in a fairly homogeneous 

 matrix. 



Greenwood (9) terms these deeply staining granules macro- 

 somes, and describes in addition to these other minute granules 

 which do not stain deeply with haematoxylin but do so with 

 borax carmine. These latter she calls microsomes. In my 

 preparations with borax carmine the nucleus seems to have 

 a finely granular appearance, but the large granules (i. e. 

 Greenwood's macrosomes) do not combine with this stain. 



In preparations stained with iron haematoxylin the macro- 

 somes are seen to be present in both the commissures and lobes 

 of the nucleus ; but if the commissures are very narrow they 

 are confined to the lobes alone. The macrosomes var\' in 

 size from minute dots barely visible at a high magnification 

 to masses up to 10 )a or more in breadth (PI. 22, figs. 1, 2, and 3). 

 Often these granules are surrounded by lightly staining areas. 

 Since these are not always present it is possible that they are 

 due to the fixative and are not to be interpreted as part of 

 the normal nuclear structure. The macrosomes vary greatly 

 in shape ; they are generally round, but may be oval, pear- 

 shaped, or even roughly oblong. The medium-sized granules 

 often show a single vacuole in the centre (PI. 22, fig. 1, vac), 

 whilst invariably wdthin the large masses one or more vacuoles 



