124 Darwin, and after Darwin. 
all round the circumference of the pellucid envelope, 
as represented in this illustration (Fig. 32). 
In thus saying that the ova of all animals are, so : 
far as microscopes can reveal, sudstantially similar, I 
am of course speaking of the egg-cell proper, and 
not of what is popularly known as the egg. The egg 
of a bird, for example, is the egg-cell, p/ws an enor- 
mous aggregation of nutritive material, an egg-shell, 
and sundry other structures suited to the subsequent 
development of the egg-cell when separated from the 
parent's body. But all these accessories are, from 
our present point of view, accidental or adventitious. 
What we have now to understand by the ovum, the 
egg, or the egg-cell, is the microscopical germ which I 
have just described. So far then as this germ is 
concerned, we find that all multicellular organisms 
begin their existence in the same kind of structure, 
and that this structure is anatomically indistinguishable 
from that of the permanent form presented by the 
lowest, or unicellular organisms. But although anato- 
mically indistinguishable, physiologically they present 
the sundry peculiarities already mentioned. 
Now I have endeavoured to show that none of 
these peculiarities are such as to exclude—or even so 
much as to invalidate-the supposition of develop- 
mental continuity between the lowest egg-cells and 
the highest protozoal cells. It remains to show in this 
place, and on the other hand_ that there is no breach 
of continuity between the lowest and the highest egg- 
cells; but, on the contrary, that the remarkable 
uniformity of the complex processes whereby their 
peculiar characters are exhibited to the histologist, is 
such as of itself to sustain the doctrine of continuity 
