68 
Blackman and Tansley. 
8. Vlatydorina. Kofoid, 1899. 
Coenobium of 16 or 32 spherical cells arranged in a 
single layer, and forming a horse-shoe-shaped plate, 
with a slight left-handed spiral twist. Mucilaginous 
investment produced at posterior (heel) end into 3 or 
5 symmetrical blunt processes. Flagella of successive 
cells alternately projecting upon either face. Develop¬ 
ment by compression of a primitive cup-shaped 
ccenobium, so that the cells of the two faces intercalate. 
Gametes unknown. 
§§ Ccenobium with a definite soma. 
9. Pleodorina. Shaw, 1894. 
Ccenobium of 32, 64 or 128 spherical cells in a single 
peripheral layer within a spherical or elliptical invest¬ 
ment. Somatic (purely vegetative) cells occupying 
the anterior pole of tne ccenobium, the remaining 
(gonidial) cells larger, alone capable of reproductive 
division. Gametes unknown. 
10. — Volvox. Linnaeus. 
Coenobium of about 200 to 22000 spherical or polygonal 
cells usually connected by stout or by fine protoplasmic 
processes, arranged in a single peripheral layer within 
a spherical investment. The enormous majority of 
the cells are somatic. Parthenogonidia 1 to 16 
(usually 8), larger than vegetative cells. Androgonidia 
similar to parthenogonidia, few or very numerous, each 
forming a transitory ccenobium which may be plate¬ 
like with few, or spherical with numerous antherozoids. 
Antherozoid a reduced elongated swarmer with 
sharply pointed anterior end and green or yellow 
chromatophore. Gynogonidia few, larger than vege¬ 
tative cells. Oospores smooth or sculptured. 
Germination direct. Sexual colonies monoecious or 
dioecious, sometimes possessing parthenogonidia. / 
[The organisms belonging to this genus exhibit a remarkable culmi¬ 
nation of the coenobiate evolution of motile cells of the Chlamydomonas- 
type. While retaining the cell-type of that primitive form, Volvox , by 
the differentiation of most of the cells of its body as a true soma, has 
reached a stage of evolution comparable with that of the Metazoa, and 
only attained along the other lines of algal descent by forms far on 
amom' the higher families. In Volvox we find realised the utmost 
potentialities of the structural plan of the motile spherical coenobium, 
and on its own lines this remarkable form may fairly be said to present 
us with the unique spectacle of a “ perfect organism.”] 
(fr) PLANT-BODY NON-MOTILE DURING THE DOMINANT PHASE. CELLS UNINUCLEATE 
MULTIPLYING BY VEGETATIVE DIVISION. 
rin this section are included all those forms of the non-motile 
Protococcoideae in which repeated vegetative division is a conspicuous 
feature of the life-cycle. The separation of these forms into the two 
families of Tetrasporaceae and Pleuiococcaceae is artificial, and was 
originally made to turn strictly on the presence or absence of zoospores. 
A number of small natural groups of genera can be made out within both 
these “ families ” but knowledge does not yet enable us to bring the whole 
of the forms into any satisfactory natural arrangement. We therefore 
retain the old artificial distinction, though not strictly, and indicate some 
of the natural groups within the “ families.”] 
