274 
Proceedings of the Royal Society 
Protista from animals on the one hand, or plants on the other ; the 
second, closely related to the first, that Protista are too heterogeneous, 
and do not admit of exact definition ; hut the third and most 
potent reason has, however, simply heen that excessive specialisation 
which allows most otherwise competent students of the Protozoa to 
remain in entire indifference to the Protophytes, and the even more 
general and deplorable ignorance of the Protozoa which prevails 
among microscopic botanists. 
The present theory, however, does away with the apparent 
heterogeneity of the Protista. On the view that Protozoa and 
Protophytes alike exhibit more or less specialised and abbreviated 
forms of a common life-cycle, the thirteen groups of Haeckel* are 
seen to he hut forms of one, and there remains absolutely no 
morphological reason for their continued separation (nor for that 
matter, any physiological reason either, were such considerations, 
irrelevant as they are to morphological taxonomy, any longer 
admissible). Hor is the objection of Huxley really valid. The 
limit between Protista and Animalia remains simply that between 
Protozoa and Metazoa ; and that between Protozoa and Protophytes 
being given up, there remains no more difficulty of separating the 
higher plants than ' there was before — a difficulty which, however 
undoubted, is not increased by unitiug the lower forms. 
The thorough unity and naturalness of the Protista being thus 
obvious, they naturally fall into a series corresponding to the stages 
of the life-cycle. In the Schizomycetes and the Palmellaceas the 
resting and motile stages are almost equally prominent, while in 
Gregarines, and still more in Desmids and Diatoms, and especially 
Saccharomycetes, the encysted stage predominates. The Protoplasta, 
Foraminifera, Heliozoa, and Kadiolaria represent of course the 
predominatingly rhizopod or amoeboid stage, while the Infusoria 
represent the ciliated, and the Myxomycetes, as has heen said, the 
plasmodial. 
It may at first sight seem as if the old grouping of Protophytes 
and Protozoa were not seriously modified, since the Protophyta 
always essentially corresponded to the series of generally encysted 
forms. And so far true ; the encysted series may still he termed 
Protophytes without any serious harm. But it must he clearly 
* Die Protisten. 
