OXNERELLA MARITIMA. 
521 
cytoplasm (see PL 27, fig. 1), and it is therefore sometimes 
necessary to compress the creature slightly with the cover- 
glass in order to see its nucleus distinctly. In the living 
organism the nucleus appears as a relatively large vesicle 
surrounded by a distinct nuclear membrane, and containing a 
large central karyosome (PI. 27, fig. 1). Between the mem- 
brane and the karyosome there is a clear zone, in which I 
have not been able to make out any structure in the fresh 
state (PI. 27, fig. 1). But in fixed and stained specimens 
{PL 27, fig. 2) not only can all the structures just described 
be seen, but in addition the clear zone appears filled with 
minute chromatin granules supported on an indistinct achro- 
matic network. These appearances are very constant after 
fixation and staining in various ways, and I incline to the 
view that the minute granules in the clear zone are actually 
present — though invisible — in the living organism, and not 
produced by fixation. 
The karyosome appears to be almost homogeneous. It 
stains uniformly with ordinary chromatin stains, but in iron- 
haematein preparations it usually appears rather paler in the 
centre than at the periphery (PL 27, fig. 2). It contains no 
granules of any sort. 
As already noted, the nucleus is usually oval in outline. 
It may be noted farther that it appears to be rigidly fixed in 
position. It is not possible to displace it by slight pressure; 
and even if pressure so great be applied to an organism as to 
burst it completely and set free most of its enclosed food- 
bodies, the nucleus still remains behind in the debris of the 
body. It is probable, I think, that the axial fibres of the 
pseudopodia which cross the nuclear membrane, and stain 
more deeply than the rest, are really attached to the nucleus 
and serve to anchor it in position (see PL 27, fig. 7). 
The nucleus in the resting state is about 4 /a-b /u in greatest 
diameter, ranging from about 3*3 /x to 5*5 jx. 
The “ Central Granule.” — As I shall often have to 
refer to this important organ in the course of the ensuing 
descriptions, it seems desirable to give it a name. The term 
VOL. 02, PART 4. NEW SERIES. 36 
