CELL-FORMATION. 115 



over large surfaces, or even entirely (as in Bangia) from 

 the cell- wall, and produces a membrane on its surface ; 

 moreover, that sometimes the mucilaginous layer divides 

 into separate portions, and produces several perfect cells. 

 It is clear that in this case, again, we cannot think of the 

 formation of a nucleus for the production of the cells. 

 These facts stand in direct connexion with those above 

 described in abnormal free cell-formation. The mucila- 

 ginous layer separates from the wall, divides, and forms 

 several larger or smaller cells. These vary in size and 

 contents, from, large cells containing chlorophyll and 

 starch, 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 contents 

 forms one or more small cells, while the remainder is 

 unaltered. 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 in 

 some cases, it must not be assumed in the rest. 



In those cases where free cell-formation takes place 

 normally, as in the origin of the germ-cells in Algae, 

 Lichens, and Fungi, and of the sporangium in Achlya, 

 we can see nothing of a nucleus. The fact, as presented 

 directly to us, with the assistance of the amplifications 

 our present optical instruments effect, may in the same 

 way be most simply explained thus : that larger or smaller 

 portions 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 free 

 cell- formation, seems to me to speak against this. I have 

 seen it in Erysibe, AcJdya, Peziza, Coleoclicete, &c.; and it 

 appears to me to be also present in the germination of 

 the Zygnemacese. Two explanations may be given as to 

 this nucleus. Either it is a primary nucleus, around 

 which the cell originated, or it is a secondary nucleus 



