T 54 
W. Bernard Crozv. 
The other cytological features, too, show that they belong to this 
family. There is a perfectly typical anterior pair of contractile 
vacuoles [14], Further their chromatophore can always be traced 
to the basin-shaped type. Gonium is recorded [13] as having this 
kind of chromatophore, close investigation showing it to be made 
up of separate granules just as in Chlamydoinonas ( Chloromonas) 
alpina Wille and C. ( Chloromonas ) aalesundensis Wille. The 
beginnings of this type are seen in C. stellata [7]. Pandorinci 
and Eudorina have a bell-shaped chromatophore [20], the 
intimate structure of which probably resembles that found in 
Gonium [13]. Merton found a reticulate chromatophore in 
Pleodovina illinoisensis [11], but that this is not necessarily derived 
from the Sphcerella type is shown by the evolution of a lacunate 
chromatophore in Chlamydomonas ( Chloromonas) reticulata. The 
latter is obviously related to Chi. longistigma where the beginnings of 
lacunations are visible on the inner contour of the cup [7]. Grove 
describes the chromatophore of Pleodovina illinoisensis as cup¬ 
shaped [9], so there is probably some variability in its form. 
The Chlamydomonadaceae are, as we have seen above, gener¬ 
ally characterised by the possession of a pair of contractile 
vacuoles situated at the base of the flagella, near the anterior 
pole of the cell. It is true that exceptional species are met 
with. In Chlamydomonas pertyi there are numerous contractile 
vacuoles, but even here they are found in the usual anterior 
position. In Agloe there are more than two contractile vacuoles, 
which is merely due to the fact that besides the usual pair there 
are three accessory vacuoles [15]. Only Chlorogonium has its 
numerous contractile vacuoles distributed over the periphery of 
the cell, and, as noticed by West [21], this genus is probably more 
closely allied to the Sphaerellaceae than the typical Chlamydomon- 
adaceae, agreeing with the former in all structural details except 
in the possession of the differentiated cell-wall with its protoplasmic 
threads. In fact the vegetative cell of Chlorogonium bears a close 
resemblance to the gamette of Sphcerella. Volvox shows a varia¬ 
tion in the number of contractile vacuoles. This is, in itself, an 
important feature. Of the species investigated V. glohator has 
two to six, usually four, and V. aureus two, in each cell. More¬ 
over, the contractile vacuoles of V. glohator are found in a 
peripheral layer of the cytoplasm, in fact sometimes two of them 
and often one of them are met with in one of the protoplasmic 
threads which connect adjacent cells of the colony [12]. The 
