534 
CLIFFORD DOBELL. 
plast in the young forms of Acanthocystis produced by 
budding, he was led to advance certain views, now well 
known, on the phylogeny of the centrosome. These views 
depend, for their validity, upon the assumptions (1) that his 
observations on the Heliozoa were correct (those relating to 
the buds — the most important for his speculations — have 
never been confirmed) ; (2) that the centroplast and the 
centrosome are homologous organs ; (3) that the Protozoa,, 
being “primitive animals, ” furnish us with data for deter- 
mining the phylogeny of the Metazoa. As regards the first 
assumption, I would merely note that the observations in 
question have been confirmed in part only. As regards the 
third, I will only say that I regard it, as I have elsewhere 
pointed out (1911) as wholly unjustifiable. Concerning the 
second assumption I shall here say a few words. 
For reasons which I have given elsewhere (1911), I do not 
regard any single protozoon as the homologue of a metazoan 
cell. A single individual lieliozoon — e.g.an Oxnerella — 
is, in my view, comparable with a single whole metazoon, and 
not with one of the cells of which it is composed. An 
Oxnerella is a whole non-cellular organism, whilst a meta- 
zoon is a similar whole organism whose body is differentiated 
into cells. The one displays a non-cellular, the other a 
cellular, morphological composition. It follows, therefore, 
that we have no reason to assume that those organs and 
structures which are peculiar to the cell must have a morpho- 
logical counterpart in the individual protozoon. 
Now the centroplast of Oxnerella and other similar 
Heliozoa is not an organ whose activities are limited to a 
transient phase in the life of the organism — the momentary 
process of division. It is, on the contrary, a complex struc- 
ture, permanently present, which plays a skeletal part in the 
organism as a whole, and in connexion with its organs of loco- 
motion and prehension, and a totally different part as an 
accessory to the process of division. It plays the part of a 
centrosome, but it does much more. On the other hand, it 
seems probable that the centroplast of multinucleate Heliozoa 
