154 Lloyd Williams . — Studies in the Dictyotaceae. 
are always about sixteen in number. Their form is curved just like those 
of the stalk-cell division. During the anaphase stage the membrane 
persists up to a very late period (Fig. 33). The mantle-fibres, centrosomes, 
and radiations are very distinct ; in fact all the accessory structures are 
far more easily seen here than in the preceding mitoses. 
The curved chromosomes aggregate at the poles in the usual way 
with their free ends towards the equator ; a membrane is formed ; then, 
as in the stalk-cell division, they lose their polarity but remain distinct 
enough to be countable for some time longer. Here (Fig. 33) again it is 
seen that the number is the reduced one. The centrosomes and radiations, 
together with the connecting fibres, are still clear. A striking feature 
of this and of the next stage (Fig. 35) is the projection of the nuclear 
membrane towards the centrosome, already seen in some previous stages. 
Fig. 34 shows the chromosomes to be accompanied by a distinctively 
staining body which in all probability is the rudiment of the nucleolus. 
The fusion of the chromosomes goes on at first somewhat like that of 
the stalk-cell division. Here, however, two masses are formed (Fig. 35), 
of which one is larger and more irregular in form than the other. A 
reticulum also appears which at first stains but faintly. Later on the 
smaller of the two masses dwindles in size and finally disappears, the 
reticulum at the same time becoming more deeply stained and the other 
body (the nucleolus) assuming a spherical form. 
Abnormalities. 
There are various abnormal developments here which it might be 
profitable to study in greater detail : — 
(1) Undivided tetraspore mother-cells are sometimes liberated, and 
several instances have been observed of their nuclei in the prophase or 
even in the spindle stage. Most of these, however, were evidently arrested, 
and there is as yet no evidence to show whether karyokinesis was initiated 
before or after separation from the thallus. 
(2) Several instances have been seen of liberated sporangia containing 
two spore-like bodies, each, however, being invested with a cell-wall. In 
one case the nuclei seemed to be in second division prophase, with spirem 
and fibrillar nucleolus. In the other the late anaphase stage was seen 
but the chromosomes could not be counted. 
(3) This is an abnormality which is of greater interest, as it occurs more 
frequently and may possibly be of some utility to the plant. 
Towards the close of the season, instead of dividing in the usual manner 
to form tetraspores, the mother-cell, without greatly increasing in size or 
taking on a deeper colour, divides into two and then into a small mass of 
parenchyma. Richards 1 observed this phenomenon in D. ciliata , but says : 
1 Proc. Amer. Acad., 1890, p. 83. 
