Burnett on Organic Relations of Infusoria, ete. — 391 
In these studies, two questions are constantly presenting 
themselves, concerning these minute forms, namely, — 1st. Are 
there any definite characteristics whereby that which is of an 
animal, can always be distinguished from that which is of a 
vegetable nature? 2d. With regard to those of an animal 
nature, what do they need, that they may be regarded as 
true animals, having individualities of their own complete ? 
I do not think, that, in the present state of our knowledge, 
either of these questions can be decided; nevertheless, we 
already have data sufficient to enable us to decide satisfac- 
torily in many instances, but the data most precious have 
not yet been found. 
It is well known that many of those distinctions hitherto 
insisted upon, as to animals and vegetables, are now regarded 
as invalid ; such, for instance, was motion, which was sup- 
posed to belong to animals and not to plants, but this is now 
known not to be the case. It was then, and is now urged, 
that voluntary motion is to be the distinctive feature; but this 
appears to obscure the matter still more, for individuals can 
never agree as to what, in these minute particles, is voluntary 
and what is involuntary. And in particles, which, from 
every reason, I have believed to be vegetable, I have seen 
motions just as adaptive as in other partieles which I had 
equally as good reasons to believe were animal. c 
In regard to the 2d question, — What characteristics 
in organic animal matter shall constitute it an individual, I 
feel satisfied of this much, — that cell-processes,, however 
closely interwoven they may be with the expressions of indi- 
vidual life, cannot be considered as constituting the ground- 
Work of its definition. And when I speak of eöll-processes, 
I mean their growth and development, their multiplication by 
segmentation, and their transition into tissues. I base this 
remark upon what I have observed. The ovum, for instance, 
originally a cell, and developing by the increase of cells, 
undergoes segmentation and multiplication of its contents, 
and in one sense may be said to be alive ; yet it does not 
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