A CRITICISM OF THE CELL-THEORY. 171 
cells, recent researches on cell lineages may perhaps give us 
a clue to the interpretation of the fact that blastomeres are 
in sO many cases, no more than coherent. For it is noticeable 
that wherever cell lineages, with marked isolation of the blasto- 
meres, have been described, there is a decided tendency to the 
precocious development of organs, or, at any rate, to the pre- 
cocious isolation of the primordia (Anlage) of organs. 
It seems probable that the discrete condition of the blasto- 
meres is connected with the fact, to which I alluded in the 
earlier part of this essay, that they are, from the very outset, 
specialised. They have each a definite molecular constitution 
different from the others, and, in figurative language, a 
limited part to perform, which they could not perform to 
advantage if they were conjunct with the other blastomeres 
and shared in their different molecular constitution. But 
this is a subject which I must leave for a future occasion when 
I discuss the validity of von Baer’s law of development. 
I have travelled in this essay over a great deal of ground, 
and I have necessarily had to touch more lightly on many 
topics than I should have wished. I hope that I may at 
least have succeeded in presenting my arguments in a manner 
which will make them clear to my readers, and that I have not 
been too discursive. Starting from Mr. Sedgwick’s propositions 
and accusations, I have tried to show what is or was the exact 
extent and meaning of the cell-theory ; I have tried to examine 
it and show how much was good and how much bad, and I 
have finally been led to the conclusion—which is not quite 
what I proposed to myself at the outset—that the cell concept 
is a valuable expression of our experience of organic life, both 
morphologically and physiologically, but that in higher or- 
ganisms cells are much what von Sachs declares them to 
be, not independent life units (Lebenseinzelheiten), but a 
phenomenon so general as to be of the highest significance ; 
they arethe constant and definite expression of the forma tive 
forces which reside in so high a degree in organic matter. 
Lest I should appear to have minimised the importance of 
the cell too much, let me conclude by saying, that nothing 
