140 Proceedings of the Royal Physical Socvety. 
while the cell B, rich in cell-plasm, will form proportionally 
larger amounts of the substances cand d. We know further, 
from my researches on the “Embryo-sac of Angiosperms,” 
that each daughter-cell commences to feed a long time before 
separation from its sister-cell has taken place, and therefore 
there is nothing to hinder a ready interchange of substances 
between the two daughter-cells A and B. This interchange 
being of direct benefit to both individuals, will tend to prevent 
a complete separation of the cells A and B; thus a unicellular 
organism will become a two-celled one, and by a repetition 
of the process just suggested, we may derive the higher 
multicellular organisms from originally unicellular ones. 
WHAT CONSTITUTES INDIVIDUALITY AMONG METAZOA ? 
We began our consideration of unicellular organisms 
by defining the terms “individual” and “cell,” and it was 
found that these two terms were co-extensive amongst 
Protozoa and Protophyta; but amongst beings consisting of 
more than one cell, a new definition of the term individual 
is required. Why then is a Hydra, a Starfish; or a Begonia 
plant termed an individual, and how is it that parts of these 
organisms may give rise, under certain conditions, to new and 
entire. beings, which are in all respects identical with the 
respective mother individual ? 
I endeavoured to show that a multicellular condition is 
the outcome of evolved metabolism, and we may therefore 
define a multicellular individual as a being in which the 
various processes necessary for life are distributed amongst a 
collection of cells, instead of being performed by the various 
organs of a single cell. Thus if we represent in a protozoan 
individual the functions of the various cell organs and their 
equilibrium by the letters A+B+C, then in a Metazoon con- 
sisting of three cells, an ideal division of labour might be 
shown thus: ABc+ABc+ ABC, the capital letter standing for 
the special function performed by each cell. Further, 
should a Metazoon have the same functions, but consist of 
more than ‘three ‘cells, then we would have to write: 
(Apc)"+(aBc)?+(ABC)". In this latter case we must 
