STRUCTURE.] CELL-FORMATION. 29 



this conclusion. They are, however, equally reconcilable 

 with the next view (D.) 



An Algal called Vesiculifera concatenata by Hassall, ' ' occurs 

 in ponds on a common near Bristol, and is of a pleasant pale 

 apple-green colour. The cells are usually from five to seven 

 times as long as broad, and are lined with but a small 

 quantity of endochrome, which is disposed in a reticulate 

 manner. Some of the cells, however, may be observed to be 

 slightly inflated, and to contain a larger amount of endo- 

 chrome than the rest ; in each of these inflated cells a spore 

 is subsequently formed, and in the following way : The en- 

 dochrome, after attaining a certain degree of density from an 

 increase in its development, not from any derived from a 

 contiguous cell, moves towards one end of its cell ; it (the 

 endochrome) shortly becomes divided into two very unequal 

 portions, the larger and terminal one of which becomes con- 

 verted into the spore, and the smaller portion is found to be 

 separated from this by a single septum. A process has, in 

 reality, taken place analogous to the fissiparous division of 

 the cell of Zygnema ; two cells have been formed within the 

 original one, but in the Vesiculifera one of these new cells is 

 the spore. In V. sequalis, I have been able to trace the 

 mode of development of the two or three contiguous spores, 

 which are sometimes to be seen in the filaments of this 

 species : the first spore is formed in the way I have pre- 

 viously mentioned, and arrives at considerable maturity 

 before there is any appearance of one, contiguous to it, 

 being produced ; b\it it may then be seen that the smaller 

 portion of endochrome, which had been separated just previ- 

 ously to the first spore being formed, and which then occupied 

 but little space in the cell, has become considerably increased 

 in amount. An increase having also taken place in the 

 length of the cell : at length the process of division, &c., 

 occurs as before, and a second spore is formed adjoining the 

 first. The formation of a third spore involves a similar chain 

 of phenomena." (Annals of Natural History, vol. xvii. p. 334.) 

 D. Cells are produced by a stricture of the sides of an original 

 cell, which stricture eventually divides the latter into two 

 cavities. This view is supported by the evidence adduced by 



