Nemalion miiltifidum , Ag. 329 
meanwhile losing in density. Cell division occurs while the chromatophore 
is in condition b or c. 
After'the first cell division, the chromatophore left in the segment will 
follow the line of development shown in Fig. 8, e, since this cell is always 
to remain buried within the thallus. While the outer region of the 
chromatophore is growing in size and developing projections which reach to 
the periphery of the cell, the central region becomes larger and the threads 
become more open and loose. The pyrenoid then begins to appear, at first 
small, then increasing in size, until at maturity it occupies about one-half 
of the area. 
The apical cell meanwhile continues to divide and re-divide until the 
limit of growth is reached. Division then ceases. The chromatophore of 
the apical cell is in stage b or / of Fig. 8. Stage / differs from stage c in 
that the central region is very densely granular and shows no tendency 
towards a thread-like arrangement. This chromatophore now takes the line 
of development^*, h. As it enlarges, the outer zone puts forth projections 
in exactly the same manner as shown in d. The central region, however, 
becomes less granular and more homogeneous (Fig. 8, g). The pyrenoid 
then makes its appearance (Fig. 8, Zi) as a small, round, dark body, which 
rapidly increases in size until, in the mature cell, it has the appearance 
shown in Fig. 9. We see, therefore, that the chromatophore may develop 
in* different ways depending upon its position in the thallus. If we were to 
trace the development of a chromatophore in one of the middle cells of the 
filament, we should find it taking a course midway between the two 
described. Every degree of difference can be found. 
Division of the chromatophore is by simple elongation and constriction. 
If it is in the condition shown in Fig. 8, c or / the granular portion con- 
stricts first, then the outer portion. Chromatophores which are older than 
this commonly do not divide, the only exception being where a mature cell 
gives rise to a side-bud which develops into a new filament. Everywhere 
else, however, including cystocarp and carpospore, the general rule holds. 
The difference between the conditions which I have just described and 
the results which Wolfe obtained are striking. Wolfe found no pyrenoid 
structures of any kind. Instead, he reported the central region of the 
chromatophore as occupied by a vacuole, entirely empty of solid contents. 
He, therefore, concluded that Nemalion has no pyrenoid or pyrenoid-like 
structure. The difference between his results and mine are due entirely to 
methods of fixation. Wolfe used only chromacetic fluids as killing reagents, 
the effect of which seems to be to destroy more or less completely the 
material of the central region. I also employed weak chromacetic to some 
extent, as well as Merkel’s fluid. With Merkel’s fluid, an appearance 
almost identical with that shown in Wolfe’s figures was obtained (Fig. 13), 
the central region nearly always being an empty hollow, the bounding wall 
