OF THE THYTOZOA. 183 



organisms. Constantly several young colonics are developed from the parent 

 at the same time, or nearly so, by the self-fi>ssion of various primordial cells ; 

 hence, as a rule, a brood of young globes is to be seen revolving ^^ithin the 

 parent sphere (XX. 33), from which ere long it is released by its rupture. 



The condition of the individual cells of a young Volvox has akeady been 

 mentioned, — viz. their close apposition at first, their gradual separation by an 

 interval, the appearance of radiating processes from the protoplasm, and their 

 progressive attenuation. To this account we may add that contiguous inter- 

 current processes, in their earher stages, appear to coalesce, — a circumstance 

 which indicates that the protoplasm is then unenclosed by a pellicle or envelope. 

 Again, the protoplasm gradually contracts itself into its flask-shape, the retrac- 

 tion and coalescence of its processes being a simultaneous phenomenon ; indeed 

 contraction of the protoplasmic globules advances continuously until, as in old 

 specimens, only a small rounded mass appears in the centre of a large clear 

 space. Lastly, the coloured stigma is an after- production ; and its advent 

 would seem to indicate the maturity of the cell. 



Analogy with other Volvocinece would lead us to look for a quiescent or 

 ^' still " stage of the cells of Volvo.v, and the formation of microgonidia, in 

 addition to the process described, viz. multiplication by self-division with 

 the production of macrogonidia. That a '' still " form actually occurs is 

 pretty clearly shown by Mr. Busk's observations of Volvox aureus, from 

 which this presumed species appears to be nothing more than Volvox glo- 

 hator, having a vaiying number of its cells encysted to form the winter or 

 '■resting" spores. The primordial cells which are to undergo this change 

 are at first indistinguishable fi^om the ordinary ones, except in having a 

 deeper green colour {Bv£c, op. cit. p. 38). Afterwards, however, they ac- 

 quii^e a thick wall, change to a yellow colour (hence the appellation aureus, 

 golden or yellow), without material alteration of size, and produce a second 

 equally fiim and distinct envelope ; or rather, it may be, the original cells 

 contract somewhat, and then form a second coat around themselves. Even- 

 tually a considerable space exists between these two coats, occupied by a 

 clear and apparently aqueous fluid ; but upon the addition of a solution of 

 iodine, a granular cloudiness is produced in it. The contents of the inner 

 cell consist chiefly of amylaceous grains, mixed with a greenish material in 

 the one case, and with a bright yellow, apparently oily fluid in the other. 

 The amylaceous particles are of an irregular botryoidal form, and far from 

 uniform in size. 



Mr. Currey, in a recent interesting communication on fresh-water AlgSB 

 (J. M. S. 1858, p. 208), states that he has seen " one of the large, orange- 

 coloured spores of the so-called V. aureus, which is only the resting form of 

 F. glohator, where the contents divided into five globular colourless cells, 

 which floated in a mass of reddish plasma, being apparently the remains of 

 so much of the original contents of the cell as had not been absorbed in the 

 formation of the secondary cells." 



Of the Volvox steUatus, Mr. Busk adds that it seems to him merely a modi- 

 fication of V. aureus, and appears to follow the same course of change, and 

 doubtless of future development. With these conclusions Prof. Williamson 

 coincides, and remarks (oj). cit. p. 56) that " the ordinary power of gemma- 

 tion in V. steUatus appears to have worn itself out, since, though the gemmae 

 often exist with the spores (?), they are small, coloiuiess, and abortive." 



It must also be mentioned that Perty suggests an analogous interpretation 

 of the nature of Volvox aureus, and doubts hkewise the specific importance 

 of V. SteUatus. 



8ince the above remarks were penned, Cohn's researches on Volvox glohator 



