66 o Blackman.— The Primitive Algae 
This specific constancy in the most primitive type is in 
strong opposition to the idea of wide polymorphism brought 
forward by Hansgirg, Chodat, and Borzi, which associates 
different genera, and even members of different families, in the 
life-history of one individual. 
Dill’s paper contains further work of importance on the 
nature of the divisions by which the different species multiply 
vegetatively. We shall find, when discussing subsequently 
the relation of the Chlamydomonads to organisms of a de¬ 
cidedly animal character, that it is a marked characteristic of 
the division-process in the latter that this takes place in the 
antero-posterior direction, being generally a slow constriction 
starting at the two ends and proceeding to the centre. 
In organisms of a decidedly vegetable character, division 
is a more rapid process, nearly simultaneous throughout the 
protoplast, and the first division nearly always takes place 
in a transverse plane. 
In Chlamydomonas, Dill finds that, while the majority of 
species divides by a rapid transverse division, ^ yet some 
divide by a first longitudinal division, not however of the 
nature of a slow constriction. The real interest of these two 
directions of division lies in this, that it is just those species 
which on evidence drawn from their sexual reproduction 
appear most primitive (i. e. least decidedly vegetal in cha¬ 
racter) that exhibit this more animal characteristic of a first 
longitudinal division. Between the species which divide 
-first transversely and those which divide first longitudinally, 
Dill discovered a small interesting group of species in which 
a transitional condition occurs. In these forms the first sign 
of division is in the longitudinal direction, but the protoplast 
gradually rotates inside the cell-wall so that the division-plane 
separating the two sister-cells becomes transverse. 
Still more striking than the variation in cytological 
characters found in the single genus Chlamydomonas is the 
variation in the sexual reproductive process. In every other 
genus of plants throughout the vegetable kingdom, however 
various the specific forms and biological characters, it is 
