CELL-FORMATION.

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over large surfaces, or even entirely (as in Bangia) fromthe cell-wall, and produces a membrane on its surface;moreover, that sometimes the mucilaginous layer dividesinto separate portions, and produces several perfect cells.It is clear that in this case, again, we cannot think of theformation of a nucleus for the production of the cells.These facts stand in direct connexion with those abovedescribed in abnormal free cell-formation. The mucila-ginous layer separates from the wall, divides, and formsseveral larger or smaller cells. These vary in size andcontents, from large cells containing chlorophyll andstarch, to the most minute cells inclosing merely homo-geneous mucilage. This mode of cell-formation varies,besides, from that condition in which the whole cell-con-tents partly form new cells, the remainder being dissolved,to that in which merely a small portion of the contentsforms one or more small cells, while the remainder isunaltered. These transitions show that all the pheno-mena of abnormal cell-formation are related to one law,and that since the formation of nuclei is inadmissible insome cases, it must not be assumed in the rest.

In those cases where free cell-formation takes placenormally, as in the origin of the germ-cells in Algae,Lichens, and Fungi, and of the sporangium in Acldya,we can see nothing of a nucleus. The fact, as presenteddirectly to us, with the assistance of the amplificationsour present optical instruments effect, may in the sameway be most simply explained thus ■. that larger or smallerportions of the contents at once become individualized,and acquire a membranous investment. But the circum-stance that a nucleus may sometimes be perceived subse-quently, in the germ-cells which have originated by freecell-formation, seems to me to speak against this. I haveseen it in Erysibe, Adilya, Peziza, Coleodmle, &c.; and itappears to me to be also present in the germination ofthe Zygnemaceae. Two explanations may be given as tothis nucleus. Either it is a primary nucleus, aroundwhich the cell originated, or it is a secondary nucleus