20 GEORGE BIDDER. 
acid alcohol, shows more often a fine, stained, tapering point, 
forming a distal prolongation to the nucleus, issuing through the 
pupil of the iris as the flagellum (cf. cut,d). In the nuclei of a 
preparation treated with 4 per cent. osmic acid, stained in bulk 
with borax-carmine, and on the slide with hematoxylin, the two 
forms are also seen: where the nucleus is spherical the flagellar 
radix is seen as a faintly-stained thread piercing the dark 
nuclear membrane (cf. cut, c); where the nucleus is pointed, 
the point—that is, the radix of the flagellum—can often be seen 
to be a protrusion of the nuclear membrane. In either case the 
nuclear membrane is interrupted, so that in profile the outline 
shows a clear break opposite the flagellum. 
In S. raphanus, treated with iodine followed by alcohol 
and borax-carmine, there is often a comparatively thick stained 
thread passing from the nucleus to the flagellum. In the same 
species, preserved in weak alcohol gradually strengthened, and 
stained in borax-carmine, very many of the nuclei appear 
pear-shaped, the distal half of the nucleus being a cone with 
its apex in the centre of the intrachoanal area. 
In these last sections many of the cells have the nuclei 
filiform and ribbon-shaped, so that they probably do not give 
the living form; and in the cell shown in fig. 5, treated with 
weak alcohol under the microscope, showed the “ vacuole ” 
perfectly spherical, refracting, and absolutely distal. But the 
particular form of distortion described, assuming it distortion, 
points to a firm mechanical connection between flagellum and 
nucleus. It seems likely that the spherical nucleus, with a 
filiform radix issuing from it, represents an unaltered living 
structure ;! we have then to consider whether the pear-shaped 
or bulb-shaped nucleus, which all additional reagents tend to 
develop represents the staining of other substances surround- 
ing the radix, or a change in form of the nuclear membrane. 
All that can be stated definitely is that the flagellum is 
firmly and intimately connected with the nuclear membrane, 
and that when this is spherical in outline the sphere shows a 
break at the point where the flagellum intersects it. The 
1 This was found to be true in the fresh tissue.—July, 1895, 
