332 ADAM SEDGWIOR. 
I am at issue with, for structures most conveniently called 
cells undoubtedly exist, as the ovum, spermatozoon, lymph- 
cells, &c.; and I fully agree that the phenomenon called cell- 
formation is very general in organic life. But at the same 
time I hold with Sachs and many others that it is not of 
primary significance, but ‘merely one of the numerous ex- 
pressions of the formative forces which reside in all matter.” 
No one who has studied animal tissues could for one moment 
deny that nuclei have in many cases a relation to the 
surrounding protoplasm, a relation which is expressed in 
the arrangement and structure of that protoplasm. They 
have not always this relation, but it is usually present, and 
the question is, how are we to interpret it? That we 
cannot interpret it finally until we know the relative values of 
nucleus and extra-nuclear protoplasm, and the functional re- 
lation between the two, is clear; but we may form and hold 
provisional theories. The hypothesis or idea which holds the 
field at the present day is the cell-theory in its modern form. 
This theory, recognising the cellular structure (while not ad- 
miring the phrase, I must use it for want of a better one) 
asserts that organisms of Metazoa are aggregations or colonies 
of individuals called cells, and derived from a single primitive 
individual—the ovum—by successive cell-divisions ; that the 
meaning of this mode of origin is given by the evolution 
theory, which allows us to suppose that the ancestor of all 
Metazoa was a unicellular Protozoon, and that the develop- 
ment of the higher animals is a recapitulation of the develop- 
ment of the race. Thus the holoblastic cleavage of the ovum 
represents the process by which the ancestral Protozoon be- 
came multicellular, and the differentiation of the cells into 
groups the beginning of cellular differentiation. According 
to this view the order is: unicellular stage—multicellular 
stage—differentiation of cells into tissue elements ; cellular 
structure preceded cell-differentiation, and to get tissues you 
must first have cells. And ten years ago it was commonly 
held that these cells were primitively separate from one another, 
and that the connections found between them in the fully 
