DesmidiecBJ] infcsobial animalcules. 233 



M. MoiTcn (see P. 18, f. 15) of the convei'sion of the propagules of 

 C. Ehrcnbergii into young fronds, that I cannot but believe a similar 

 phenomeuon to have been noticed by both observers, and am inclined 

 to accept the views of Mi-. Jcnner as the correct one, and to regard 

 propagation by Zoospores or "propagules" as one nut yet satisfac- 

 torily established in the Besmidiece.''^ (Ann. Nat. Hist. 1850, p. 4.) 



" The second mode of reproduction is by coupling {conjiigation), and 

 the fonnation of sporangia. A communication is established between 

 two cells, and a seed-like mass is formed in the same manner as in 

 the Conjugated. (See P. 1 3, figs. 5, 6, and 15.) Tliis is green and granidai- 

 at first, but soon becomes of a homogeneous appearance, and of a 

 broAvn or even reddish colour. In the family Conjugates, the cells 

 conjugate whilst still forming parts of a filament; but in the Besmidiem, 

 the filamentous species almost invariably separate into single joints 

 before their conjugation, and, in most of the species, the valves of the 

 cells become detached after they are emptied of their contents. (See 

 the account of Closterium.) In many genera the sporangia remain 

 smooth and unaltered ; in others they become granulated, tubercu- 

 lated, or spinous ; the spines being either simple or forked at the 

 apex. The sporangia I consider capsules ; and this view seems to 

 be confirmed by the experience of Mr. Jenner, who states that the 

 covering of the sporangium swells ; and a mucus is secreted, in 

 which minute fronds appear, and, by their increase, at length rupture 

 the attenuated covering. The sporangia are most abundant in spiing 

 before the pools dry up. 



" That the orbicular spinous bodies, so frequent in flint, are fossil 

 sporangia, cannot be doubtful, when they are compared with figures 

 of recent ones. Ehi-enberg describes them as fossil Xanthidia ; but 

 the true Xanthidia have compressed, bipartite, and bivalved cells, 

 whilst these fossils have globose and entire ones. In all the Desmi- 

 diccB, but especially in Closterium and Micrasterias, small compact 

 seed-like bodies of a blackish colour are at times met with. Their 

 situation is uncertain, and their number varies from one to four. 

 In their immediate neighbourhood, the endochrome is wanting, as 

 if it had been required to form them, but in the rest of the fr'ond 

 it retains its usual colour and appearance. I camiot satisfy my- 

 self respectiag the nature of these bodies, but I believe them 



B 



