i 4 7 
Lloyd Williams . — Studies in the Dictyotaceae. 
frequently seems as if the thread were directly continuous with, or attached 
to some of the cytoplasmic fibres. Very often, also, the long angular loops 
of the spirem seem to radiate from the vicinity of the centrosome towards 
the nuclear cavity. Although generally in two knots, the spirem is con- 
tinuous, one or several connecting threads stretching across the cavity from 
one knot to the other. These frequently pass over the surface of the 
nucleolus, and can be seen to be in contact with it (Fig. 8). The behaviour 
of the latter is interesting. It invariably becomes swollen, very irregular 
in shape, and greatly vacuolated, btit never fibrillar. Many cases are seen 
where a portion is drawn out towards the spirem, to which the apex of the 
projection is attached (Figs. 9, 10). Sometimes big roundish lumps appear 
to be on the point of separating from it, and at others the whole nucleolus 
seems to be fragmenting. This, however, it never does ; as soon as the 
synapsis is over the nucleolus resumes its spherical form. Fig. 9 shows 
a case where there is only one knot. It sometimes happens that the 
spirem is entirely on the basal side of the nucleus (i. e. on the side nearest 
the ‘ basal ’ or ‘ stalk-cell ’) and not in the vicinity of the poles. In Padina 
it is most frequently either on the basal or on the distal side, or both. This 
has probably some reference to the fact that here the sporangia are com- 
pressed laterally by contact with each other, so that the axis of the first 
division spindle is vertical to the surface of the thallus instead of parallel to 
it as in Dictyota. 
The other constituents of the nucleu^at this period are the spherule 
above described and a small quantity of cloudy nucleoplasm, which on 
closer examination resolves itself into a very fine reticulum which, however, 
stains but slightly. 
The staining reactions at this stage are as follows. The spirem, 
spherule, and the physodes stain deeply with the chromatin stain, the two 
latter often showing different shades of colour. The nucleolus, chloro- 
plasts, and cytoplasm take the basic stain, the two former more deeply 
than the latter. 
It is very evident that there is an intimate relation between the spirem 
and the cytoplasm at this stage, and that communication between them 
is chiefly localized at the poles. The frequent connexion between the 
nucleolus and the spirem, as well as the poverty of the former in chromatin, 
both seem to indicate that much, if not all, of the chromatin comes out 
of the nucleolus. 
The Beaded Spirem Stage. The thread now becomes thicker, and 
the chromatin discs can more easily be seen (Fig. 11). The knots loosen 
out and the thread becomes distributed more uniformly over the membrane 
on the basal side of the nucleus, more rarely over the upper side. The 
cloudy nucleoplasm is also generally aggregated along the basal side, 
so that the spirem seems embedded in it. The nucleolus gradually 
