664 Lewis . — The Life History of Grijfithsia Bornetiana. 
A third and sometimes a fourth mother-cell may be formed in the same 
way. The first mother-cell may be regarded as terminal, the other as 
lateral. 
In rare cases, two nuclei occur in the primary tetrasporic cell from its 
inception, and in one case, at least, two nuclei have been noted in the very 
young tetraspore-mother-cell. This recalls the suggestion of Heydrich ( 41 ) 
of a possible sexual significance of the tetraspore. Examination of a large 
series of developing tetraspore-mothcr-cells convinces me, however, that 
there is here a purely accidental phenomenon, which has no place in the 
normal life-history, and which is not to be considered as analogous in any 
way to the sexual process. 
The cells of the tetrasporic branch appear at first not to secrete 
cellulose walls of their own. The stalk-cell, with its tetraspore-mother- 
cells, remains surrounded by the gelatinized wall of the vegetative cell on 
which it is borne. This wall, much swollen, covers the tetrasporic branch 
completely (Fig. 107). It continues to swell, and by the time the spores 
are ready to be discharged it seems to dissolve largely or completely in the 
sea-water. 
The stalk-cell increases in size, and its nucleus at the same time 
divides by successive mitoses until usually sixteen daughter-nuclei are finally 
produced. With the growth of the cell in size, the cytoplasm becomes less 
dense, and vacuoles appear in it. There may be a single large central 
vacuole, or several smaller ones variously disposed. The connexion of the 
stalk-cell with the vegetative cell, and also with the tetraspore-mother-cells, 
is of the usual type. On the side toward the stalk-cell the cytoplasm of 
the mother-cell is produced into a rather narrow strand, which meets a 
similar strand from the stalk-cell at the point where the callus-like plugs 
are developed (Fig. 109). 
It sometimes happens that the stalk-cell produces laterally a tubular 
process that curves up around the mother-cells and resembles in appearance 
an involucral ray (Fig. no). This recalls the condition in Griffithsia 
barbata and other species, in which the tetraspores are borne laterally on 
short involucrate ramuli. 
The tetraspore-mother-cell increases in size, the nucleus showing cor- 
responding enlargement. The cytoplasm begins to show numerous small 
vacuoles between the rather dense cytoplasm surrounding the nucleus and 
that lying in the periphery of the cell. 
The behaviour of the nucleolus during the period of enlargement of the 
nucleus is interesting. As the nucleolus increases in mass, it fragments 
into several rounded bodies of various sizes (Figs. 107, 108). This process 
of fragmentation continues until from 12-14 rounded masses of chromatin 
of about the same size are formed (Fig. m). These lie in a clump in the 
centre of the nucleus, staining very heavily with nuclear dyes. 
