304 ADAM SEDGWICK. 
escaped observation. But, on the other hand, there was the 
possibility that the completely segmenting ova were secondary 
acquisitions of ontogeny, and that the development in such 
forms as Peripatus, Alcyonaria, &c., was more primitive, and 
that the passage from a Protozoon to a Metazoon had taken 
place by way of a form more resembling a multinucleated 
cilated Infusorian than Volvox. In other words, that the 
differentiation of the Metazoa had been effected in a continuous 
multinucleated plasmatic mass, and that the cellular structure 
had arisen by the special arrangement of the nuclei in reference 
to the structural changes. This was the stage to which my 
researches on Peripatus led me. Since then I have paid 
attention to Vertebrata, and I have found that a number of 
embryonic processes have been wrongly described, amongst 
them such important matters as the development of nerves 
and the origin of the mesoderm ; and I thought that I traced the 
errors referred to to the dominating influence of the cell-theory 
in its modern form, for the facts seemed so obvious in them- 
selves that it would have been impossible to make any mistake 
about them had they been examined without the prejudice 
imparted by a preconceived theory. A theory which led to such 
obvious errors must, I thought, be wrong, and I denounced it. 
But my denunciation in no way implies that I fail to recognise 
the so-called cellular structure of organisms or their origin 
from the one-celled ovum. On the contrary, I was led toa re- 
consideration of the question, what is the meaning of the pre- 
dominance of the structure called cellular, which is characterised 
by a definite relation of the nuclei to the functional tissues, 
and of the fact that the organism so often passes through a 
unicellular stage. With regard to the former I must say 
that I have arrived at no conclusions which enable me to 
formulate to myself any satisfactory hypothesis, and, as 
I stated at the outset, I do not think it is possible 
to do this until we acquire some more understanding of 
the relative function of nuclei and protoplasm, But with 
regard to the latter there are some facts which might 
well be considered. In the first place, the unicellular origin 
