of Edinhurgli, Session 1883-84. 
269 
cellular unit, however valuable, yet throws no light upon a large 
number of problems at present under dispute ; and it is the aim of 
the present paper to draw attention to some of these, and by the 
aid of a re-statement of the cell theory (a new appendix as it were 
to the Anatomie Ghi'erale, or to the work of Schwann), to propose a 
solution of them. 
The problems then which it is proposed to discuss may he briefly 
enumerated for convenience under separate heads, as follows : — 
(1) The classification and affinities of the Protozoa. 
(2) The classification and affinities of the Protophytes. 
(3) The systematic position of the Myxomycetes and other 
peculiar forms. 
(4) The acceptance or rejection of Haeckel’s third intermediate 
sub-kingdom Protista. 
(5) The phytogeny of the low^er plants and animals, and their 
origin from one or several stocks. 
(6) The relation of the Protophytes to the higher plants. 
(7) The relation of the Protozoa to the higher animals. 
(8) The morphological relations of plants to animals and their 
origin from a common stock, or from separate ones. 
(9) The classification of animal tissues. 
(10) The physiological rationale of changes of cell-form. 
(11) A theory of the origin of sexual reproduction, and its relation 
to conjugation and other cases of cell union. 
(12) The relation between normal and pathological tissues. 
(13) The influence of the environment on the origin of organic 
forms. 
(14) A theory of cellular variation (since the theory of descent 
involves a theory of variation, and all variations, normal and patho- 
logical alike) must ultimately be expressible in terms of cellular ones. 
1. Classification and Ajfinities of the Protozoa. — The Protozoa 
have long been thrown into a few main groups, of which the Rhizo- 
poda, embracing all essentially amoeboid forms like the Protoplasta, 
Foraminifera, Heliozoa, and Eadiolaria, and the Infusoria, including 
all those of permanent and usually ciliated type, are the oldest and 
most important. The position of the Gregarinida, of the Monads, 
and still more of forms like Chlamydomyxa and the Labyrinthulida, 
