CELL-FORMATION. 99 



geneous, colourless mucilage. The next and most important 

 change which will occur in it is the appearance of an en- 

 veloping layer of membrane. 



In fig. 3 is also represented a portion of an old utricle 

 of Bryopsis Balbisiana. With the decaying and dissolv- 

 ing contents (chlorophyll, starch, and mucilage) occur 

 small and large cells in various stages. Some are very 

 small, and do not differ in appearance from a drop of 

 mucilage (a, a] ; others are somewhat larger, finely 

 granular, greenish, and already exhibit a delicate mem- 

 brane (b, b) ; others again are tolerably large and green, 

 with a distinct membrane (c, c). 



Under the head of free cell-formation without a visible 

 nucleus, the origin of the germ-cells (spores) of the 

 Zygnemacese (Spiroyyra^ Zyynema, &c.) must also be 

 mentioned. The facts of the case are well known ; that 

 two cells unite together (conjugate) ; that the septa of 

 the point of junction become dissolved ; that the contents 

 of the two cells separate from their walls, and, either in 

 the cavity of one of the two cells, or in the tube connect- 

 ing them, become agglomerated into a globular or ellip- 

 soidal mass, which becomes the germ-cell. All that 

 observation shows, in reference to the last proceeding, is, 

 at first, a mass of green cell-contents, with a definite out- 

 line, and subsequently the same mass of green contents 

 inclosed in a membrane. There may be two hypotheses 

 as to the formation of this membrane : 1, that it origi- 

 nates in the place where it first becomes visible on the 

 surface of the contents ; 2, that it originates as a minute 

 cell in the interior, and, as it increases in size, gradually 

 absorbs the contents. 



In favour of the first assumption speaks, in the first 

 place, the analogy with the abnormal cell-formation in 

 Bryopsis, Conferva, &c., where the membrane is in like 

 manner formed over the surface of the contents. More- 

 over, an additional support is derived from the circum- 

 stance that we can see nothing of any little cell in the 

 interior, or of the alterations in the contents (solution and 



