Carter . — S Hedies on the Chloroplasts of Desmids. IV. 31 1 
chromatophores. Each nucleus finally takes up its position in the con- 
striction, and the chloroplast then completes its division, the nucleus slipping 
in between the two newly-formed halves. 
In Hyalotheca according to Acton ( 1916 ) it is the nucleus which 
divides first, and the transverse wall is then formed. As in Closterinm the 
daughter nuclei then become amoeboid, and each one takes up a lateral 
position opposite the central pyrenoid of one of the chloroplasts. Under 
the influence of the nucleus the chloroplast and pyrenoid now divide, the 
nucleus slipping in between the two halves of the chloroplast as they 
separate. 
The process in Hyalotheca differs from that in Closterium in that the 
chloroplast does not divide until after nuclear division has been completed, 
whereas in Closterium the chromatophores prepare for their division long 
before there are any other visible signs of cell-division. On the other hand 
the two genera agree in the amoeboid movements of the daughter nuclei. 
During the present investigation the process of cell-division was studied 
in living examples of several species, including Micrasterias rotata , (Grev.) 
Ralfs; M. denticulata y Breb.; Cosmarium punctulatum, Breb.; C. subtumi - 
dum, Nordst. ; Euastrum Didelta , (Turp.) Ralfs ; Eu. ansatum , Ralfs; and 
Staurastrum punctidatum , Breb., whilst the division process was investigated 
* from stained preparations at various stages in several other species. 
In Netrium and Cylindrocystis cell-division probably closely resembles 
that of Closterium . In Fig. 51 the first signs of cell-division are seen in 
Netrium oblongum , (de Bary) Liitkefn., var. cylmdricum , West, in the con- 
striction of the chloroplast and pyrenoid about half-way between the nucleus 
and apex. (In Closterium this constriction occurs about one-third the 
distance from nucleus to apex, because the apices of the cell are usually so 
very attenuated, but in both cases the chlorophyll-bearing material is 
approximately halved.) In Fig. 53 ( Netrium Digitus ) the transverse wall 
has been formed, and the daughter nuclei have begun to migrate towards 
the gaps between the chloroplasts, the latter having apparently quite com- 
pleted their division without the very close association of the nuclei. Fig. 52 
shows the completed division. 
A rather late division stage in Cylindrocystis erassa, de Bary, is seen in 
Fig. 50. The pyrenoids and nucleus have already divided, and the new cell- 
wall is beginning to form, whilst the daughter nuclei have migrated towards 
the constrictions in the chloroplasts. 
In all the constricted species examined the process of cell-division is 
quite different from that in both Closterium and Hyalotheca. There is 
never any migration of the daughter nuclei, for these, in all the forms 
examined, naturally lie, as soon as formed, one at each end of the rapidly 
elongating isthmus between the two semi-cells of the dividing individual. 
Thus from the first they occupy their normal position in the isthmus, and as 
