and the Flagellata. 65 1 
Let us now examine these three tendencies and the different 
organisms which manifest them in order to see what their 
origin may have been and whither they lead. 
1. The manifestation of the Volvocine tendency is com¬ 
prised within the single sub-family Volvoceae (Wille). This 
consists of a series of genera which are practically coenobia 
of cells of the Chlamydomonad type (see Section II). The 
other sub-families of the Volvocaceae, except Scyaminae, are 
like Chlamydomonas , strictly unicellular motile individuals 
and in the Volvoceae we find evolving from them, by the 
aggregations of such units, the ascending series of forms 
of Gonium , Pandorina , Eudorina , Plaeodorina, and Volvox. 
Volvox is undoubtedly the highest of these motile coenobia 1 , 
and has reached a very high degree of organization in that 
it has parts specialized for reproduction and a true non- 
reproductive ‘ soma.’ The sexual reproduction is oogamous, 
and Coleochaete alone among the green Algae exhibits a 
higher method. Along this line of evolution nothing higher 
than Volvox exists, and this tendency comes to a blind end 
within the Chlorophyceae, or indeed within its lowest group— 
the Protococcoideae—as generally understood. 
In its grade of organization and of reproduction Volvox is 
on a level with high forms in the Siphoneae and Confer- 
voideae, and is, I think, much too highly evolved to be included 
in a family of primitive forms. Yet it would be impossible 
to remove it from the Protococcoideae without taking out 
also the primitive Chlamydomonas , so closely are they linked 
by intermediate forms. This alone shows how unnatural is 
this e grade ’ group. 
2. The second tendency is exhibited in the Tetrasporaceae, 
where vegetative cell-division is the chief method of multi¬ 
plication, and in the Pleurococcaceae, where it is the only 
1 By a ‘ coenobium ’ is to be understood, structurally, a definite colony of cells 
which is reproduced as such from a mother-cell, and which never multiplies its 
number of units when once thus formed, so that all its cells belong to the same 
generation. Coenobia exhibit very different degrees of solidarity, individuality, 
and differentiation. 
