VOLVOX. 



[ 683 ] 



VOLVOX. 



of calcium, which might lead to an error on 

 this point, for the outer membrane is then 

 sometimes swollen into papillae opposite 

 each corpuscle (PI. 3. fig. 30), the furrows 

 between which, in certain foci, give an ap- 

 pearance of a septum running round each 

 corpuscle (PL 3. fig. 29). Similar prepara- 

 tions also often show the green corpuscle 

 contracted, and leaving an empty ring round 

 it, separating it from the gelatinous coat 

 which runs undistinguishably into those of 

 the neighbouring corpuscles. But the 

 strongest fact we have observed is, that by 

 the application of solution of potash, the 

 substance surrounding the corpuscles is so 

 entirely dissolved, that the oily substance 

 extracted from the green bodies will run 

 freely about beneath the external membrane 

 (apparently confined internally by another 

 film), in sheets extending over considerable 

 segments of the sphere, yet leaving the cor- 

 puscles and their radiating processes intact, 

 or at least only shrunk and discoloured. If 

 a true cell-membrane existed around each 

 corpuscle, forming septa dividing them, the 

 above phenomenon could not display itself, 

 since the potash would not so dissolve the 

 structures. 



The modes of reproduction of Volvox 

 have not yet been entirely elucidated. In 

 certain conditions, some of the corpuscles 

 appear larger than the rest, and as if under- 

 going division (PI. 3. fig. 28); it is possible 

 that some of the corpuscles, or of such 

 grouped corpuscles, escape into the cavity, 

 and there become developed into the large 

 green bodies (PI. 3. fig. 24), which are rudi- 

 mentary globes ; but Williams believes these 

 are detached in an earlier stage: perhaps 

 both modes of development take place. 

 Forms with the grouped corpuscles (PI. 3. 

 fig. 29) would appear to represent Ehren- 

 berg's Spharosira. Ehrenberg's genus Uro- 

 glena again would seem to be a Volvox 

 either imperfectly developed or decaying. 



The deep green bodies (PI. 3. fig. 24) 

 seen in the cavity of the spheres, are young 

 Volvoces, and in an early stage they appear 

 as spherical cells filled with granular green 

 substance; the green substance divides by 

 segmentation (PL 3. figs. 31, 32) until it 

 forms a group of corpuscles, on each of 

 which a pair of cilia appears ; the enclosing 

 membrane expands, and they follow it and 

 remove apart, until they form a perfect Vol- 

 0oa?-sphere, studded with the corpuscles. 

 As above mentioned, a second generation is 

 sometimes met with in the parent-sphere 



(PI. 3. fig. 25). We are uncertain whether 

 to regard the objects represented in PL 3. 

 fig. 14, as the young of Volvox ; they would 

 seemingly equally represent the genus Pan- 

 dorina, Syncrypta, or Eudorina, Ehr. 



Volvoces, examined in autumn and early 

 winter, often either exhibit the green bodies 

 with a thick coat (PL 3. fig. 33), or the inner 

 globes are of an orange colour (PL 3. figs. 26 

 & 34), which appear to be successive stages 

 of development of a resting -spore. When 

 mature, this possesses at least two coats, 

 one immediately surrounding the granular 

 contents, another at some distance outside 

 the former, transparent, colourless, and as 

 it were glassy and brittle, breaking with 

 sharp-angled cracks when pressed (PL 3. 

 figs. 34 & 35). We cannot detect any in- 

 termediate substance or layer, which would 

 be required to complete the analogy with the 

 resting-spore of SPIROGYRA, as described 

 by Pringsheim (PL 5. fig. 21); perhaps it 

 does not exist in either case. Sometimes 

 the outer coat of the enclosed yellow globes 

 is tuberculated or covered with conical ele- 

 vations (PL 3. fig. 36). The form with the 

 smooth yellow resting-spores (PL 3. figs. 26 

 & 34) represents Ehrenberg's Volvox aureus, 

 and the form with the spines (PL 3. fig. 36) 

 his V. stellatus. The germination of these 

 spores does not appear to have been ob- 

 served. 



A doubt remains as to the nature of the 

 object described as Synura Uvella ; it may 

 belong here, or, not improbably, to the 

 genus Uvella (PL 25. fig. 18), which itself 

 may be no more than a complex form of 

 the PROTOCOCCUS or Chlamidomonas (PL 3. 

 fig. 2; PL 23. fig. 30), which doubtless in- 

 cludes also Chlorogonium (PL 23. fig. 31), 

 Cryptoglena (PL 23. fig. 35), and Gyges 

 (PL 41. fig. 14), if not more, supposed In- 

 fusorial animalcules. 



When a pool contains Volvox, the indi- 

 viduals are generally abundant, and may be 

 readily seen by the naked eye, as pale green 

 globules, in a phial of water held up to the 

 light ; but we have never found them survive 

 more than a week or two when kept for ob- 

 servation. The cilia are best seen by drying 

 them and wetting again, or by applying 

 iodine. The character of the corpuscles 

 alters a good deal in chloride of calcium. 



BIBL. Ehrenberg, In/us.; Pritchard, In- 

 fus. ; Williamson, Trans. Phil. Soc. Man- 

 chester, vol. ix.; Trans. Micr. Soc. 2 ser. i. 

 p. 45 (1853); Busk, ibid. p. 31. See also 

 STEPHANOSPH^RA. 



