r 1 6 Darivin, and aftej- 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 cells 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 



