116 Darwin, and after Darwin. 
distinctions? Briefly, as we have seen, they are the 
extrusion from egg-cells of polar bodies, and the 
occurrence, both in egg-cells and their products 
(tissue-cells), of the process of karyokinesis. But, as 
regards the polar bodies, it is surely not difficult to 
suppose that, whatever their significance may be, it is 
probably in some way or another connected with the 
high specialization of the functions which an egg-cell 
has to discharge. Nor is there any difficulty in further 
supposing that, whatever purpose is served by getting 
rid of polar bodies, the process whereby they are got rid 
of was originally one of utilitarian development—i. e. 
a process which at its commencement did not betoken 
any difference of kind, or breach of continuity, between 
egg-cells and cclls of simpler constitution. 
Lastly, with respect to karyokinesis, although it 
is true that the microscope has in comparatively 
recent years displayed this apparently important 
distinction between unicellular and multicellular or- 
ganisms, two considerations have here to be supplied. 
The first is, that in some of the Protozoa processes 
very much resembling those of karyokinesis have 
already been observed taking place in the nucleus 
preparatory to its division. And although such pro- 
cesses do not present quite the same appearances as 
are to be met with in egg-cells, neither do the karyo- 
kinetic processes in tissue-cells, which in their sundry 
kinds exhibit great variations in this respect. More- 
over, even if such were not the case, the bare fact 
that nuclear division is not invariably of the simple 
or direct character in the case of all Protozoa, is 
sufficient to show that the distinction now before 
us—like the one last dealt with—is by no means 
