Classification of some colonial Chlamydomonads. 1 5 7 
the lamella. In V. aureus they are narrower and pass through in 
their entirety. V. tertius only shows plasma connections in the 
young unborn cells, where they resemble those of V. aureus, but 
by the time the colony becomes free these strings are no longer 
visible. Thus in three closely related species of Volvox we have 
three very divergent types of plasma-connection. Hence only the 
fundamental nature of these structures can be taken into account 
in estimating affinities ; their actual form is too variable to be 
considered. It appears, then, that they are truly comparable with 
the outgrowths of the protoplast in Sphcerella. No doubt they have 
taken on a connecting function in relation to the colonial mode of 
life of the Volvox cells; and it is easy to see how this might have 
occurred. Even in the species of Sphcerella the outgrowths exhibit 
the variations that have been enumerated above for the species of 
Volvox. Thus in 6'. droehakensis they are wide, show branching 
and just beneath the outer skin of the membrane they may divide 
up into numerous fine threads [22], The other species show fine 
straight protoplasmic processes. 
From the above facts it seems that Volvox possesses all the 
characteristic features of the Sphaerellaceae, although very distinct 
in its colony-form and sexual organs. The genus Volvox , has, no 
doubt, been evolved independently of the genus Sphcerella itself, 
but on the other hand the similarity between the colonies of Volvox 
and those of the other colonial Chlamydomonads is really quite 
superficial, The family Sphaerellaceae was founded on two genera 
Sphcerella and Stephanosphcera. The latter is a colonial type and 
although essentially similar in its protoplast shows quite a 
different type of colony organisation, in which at first sight the 
cell-wall structure is very different from that of Volvox. A com¬ 
parison of the two genera with Sphcerella , however, accounts for 
this. It seems that the colony envelope of Stephanosphcera is 
homologous with that of the individual cell of Sphcerella [Fig. 2 B]. 
Schmidle has pointed out that the only difference between 
Stephanosphcera and Sphcerella is that the former normally has 
several protoplasts within the membrane, the latter only one [17J. 
Sometimes a membrane of Stephanosphcera may contain only one 
protoplast in which case the organism is indistinguishable from 
Sphcerella [17]. In Volvox, of course, each protoplast has its 
own envelope, the whole of these investments fitting together, 
sometimes with intercellular mucilege, to form a sphere [Fig. 2 C, 
D & E]. 
