268 



THE MICROSCOPE AND ITS REVELATIONS. 



mingled so as to form a single mass (E), as is the case in many of the 

 Conjugates ( 235). The joint which contains the zygospore can scarcely 

 be distinguished at first (after the separation of the empty cell), save by 

 the greater density of its contents; but the proper coats of the zygospore 

 gradually become' more distinct, and the enveloping cell-wall disappears. 

 -The subsequent history of the zygospores has hitherto been made out 

 in only a few cases. From the observations of Mrs. H. Thomas (loc. cit.) 

 on Cosmarium, it appeared that each zygospore gives origin, not to a 

 single cell but to a brood of cells; and this view is fully confirmed by 

 Hoffmeister, 1 who speaks of it as beyond doubt that the contents of the 

 zygospores are transformed by repeated binary subdivisions into 8 or 16 

 cells, which assume the original form of the parent before they are set 

 free by the rupture or diffluence of the inclosing wall. The observations 

 of Jenner and Focke render it probable that the same is the case in Clos- 

 terium ; but much has still to be learned in regard to the development 

 of the products of the Generative process, as it is by no means certain 



Conjugation of Closterium striatulum: A 

 dinary cell; B, empty cell; c, two cells in co 

 gation, with incipient zygospore. 



A, or- 

 conju- 



Conjugation of Cosmarium botrytis : 

 A, mature cells; B, empty cell-enve- 

 lope; c, transverse view; D, zygospore 

 with empty cell-envelopes 



that they always resemble the parent forms. For it is affirmed by Mr. 

 Ealfs that there are several Desmidiaceae which never make their appear- 

 ance in the same pool for two years successively, although their zygo- 

 spores are abundantly produced a circumstance which would seem to 

 indicate an ( alternation of generations.' It is a subject, therefore, to 

 which the attention of Microscopists cannot be too sedulously directed. 



268. The subdivision of this Family into Genera, according to the 

 method of Mr. Ealfs ("British DesmidieaB "), as modified by Mr. 

 Archer (Pritchard's "Infusoria"), is based in the first instance upon 

 the connection or disconnection of the individual cells; two groups 

 being thus formed, of which one includes all the genera whose cells, 

 when multiplied by binary subdivision, remain united into an elongated 

 filament; whilst the other comprehends all those in which the cells 

 become separated by the completion of the fission. The further division 



Ann. of Nat. Hist.," 3d Ser., Vol. i. (1858), p. 2. 



