AFFINITIES AND CLASSIFICATION OF ALG. 55 
nearly related members of one series, the Cenobia, although 
placed, in a purely sexual system of classification, the first in 
Protococcacee, the second in Zygophyces, the third in Oophyces. 
In Volvox we have the culmination of the attempt of Nature 
to evolve higher organisms out of the perfection of ccnobes 
or motile families of equivalent cells. The Hydrodictyee are 
probably an aberrant member of this group ; Pediastrum I place 
elsew here. 
The further differentiation of the individual cell has advanced 
one stage in the Hremobie@ or Characiaces, an ill-defined family 
making up, together with the Protococcacem, the group of 
Protococcoidex, and including such forms as Characium, Apio- 
cystis, Codiolum, and Sciadium. From them the next step is to 
the group which I propose to call the Multinucleata, consisting 
of the Siphonocladacee and Siphonee, characterized by each indi- 
vidual consisting of an enormously developed cell, often ramify- 
ing greatly and attaining gigantie dimensions, and containing 
several, often a very considerable number of, nuclei. In the 
Siphonocladacese (placed under Zygophyces) the only known 
mode of reproduction is the conjugation of zoogametes ; its 
lowest member, Botrydium, shows a distinct affinity to Botrydina 
among the Eremobiæ ; higher developments are exhibited in such 
remarkable organisms as Bryopsis, Codium, Acetabularia, Cau- 
lerpa, Valonia, and Rhipelia. The Siphone® (usually placed 
among the Oophyce»), represented by the familiar genus Vau- 
cheria, are possibly a higher development of theSiphonocladaces, 
in whieh true sexual organs, oogones and antherids, are formed, 
in addition to non-sexual zoospores, the reproductive portion of 
the thallus being now divided off by septa. It is, however, 
equally probable, or perbaps more so, that the Siphonew have 
been derived directly from the higher Protococcoidew, and that 
the Siphonocladaces are a group in which the vegetative organs 
have attained an extraordinary development, while the sexual 
organs, represented by the oogones and antherids, are altogether 
suppressed. . 
The striving after a high development by the elaboration of a 
single cell eulminates in Vaucheria, or in such forms as Acetabu- 
laria; but the plan which ultimately proved successful was the 
formation of a filament of cells by cell-division. In the Cyano- 
phyces we have seen a rudimentary exhibition of this structure 
in the Nostochinew, but combined with other conditions which 
