VOLVOX. 



[ 814 ] 



VORTICELLA. 



forming septa dividing them, the above 

 phenomenon couldnot display itself, since the 

 potash would not so dissolve the structures. 



The modes of reproduction of Volvox 

 have recently been entirely elucidated. In 

 certain conditions, some of the gonidia ap- 

 pear larger than the rest, and as if under- 

 going division (PL 7. fig. 27) ; it is possible 

 that some of the gonidia, or of such grouped 

 gonidia, escape into the cavity, and there 

 become developed into the large green bo- 

 dies (PI. 7. fig. 24), which are rudimentary 

 globes j but Williamson believes these are 

 detached in an earlier stage : perhaps both 

 modes of development take place. Forms 

 with the grouped gonidia (PI. 7. fig. 29) 

 would appear to represent Ehrenberg's 

 Sphcerosira. Ehrenberg's genus Uroglena, 

 again, would seem to be a Volvox either im- 

 perfectly developed or decaying. 



The deep-green bodies (PI. 7. 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 (PI. 7. figs. 31, 32) until it 

 forms a group of gonidia, on each of which 

 a pair of cilia appears , the enclosing mem- 

 brane expands, and they follow it and re- 

 move apart, until they form a perfect Vol- 

 mr-sphere, studded with the gonidia. As 

 above mentioned, a second generation is 

 sometimes met with in the parent sphere 

 (PI. 7. fig. 25). We are uncertain whether 

 to regard the objects represented in PI. 7. 

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

 seemingly equally represent the genus Pan- 

 donna, Syncrypta, or Eudorina, Ehr. 



Volvox, examined in autumn and early 

 winter, often exhibits either the green bodies 

 with a thick coat (PI. 7. fig. 33), or the inner 

 globes are of an orange colour (PI. 7. 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 7. 

 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 9. fig. 21) j 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 7. fig. 36). The form with the 

 | smooth yellow resting-spores (PL 7. figs. 26 

 | & 34) represents Ehrenberg's Volvox aureus, 

 i and the form with the spines (PL 7. fig. 36) 

 I his V. stellatus. The development of the 

 ! resting-spores of Volvox has been fully de- 

 scribed by Cohn, and presents an essential 

 resemblance to the process in PANDORINA 

 I and STEPHANOSPH-ERA. Some of the 

 i gonidia become enclosed in special cyst-like 

 | coats j and their contents are then converted 

 j into spermatozoids, which break out and 

 move actively in the interior of the spherical 

 common envelope. These bodies fertilize 

 other gonidia, which take on the function 

 of spore-cells ; and after their impregnation 

 the latter acquire the firm coats and yellow 

 contents characteristic of the resting-spores. 

 They are set free at first into the common 

 cavity of the spherical envelope. 



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 32. fig. 18), which itself 

 may be no more than a complex form of 

 PBOTOCOCCUS or Chlamidomonas (PL 7. 

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

 cludes also Chloroyonium (PL 30. fig. 31), 

 Cryptoglena (fig. 35), and Gyges (PL 50. 

 fig. 14). 



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 they are kept with difficulty, 

 being devoured by ROTATORIA, &c. The 

 cilia are best seen by drying and wetting 

 them again, or by applying iodine. The 

 gonidia are a good deal altered by chloride 

 of calcium. 



BIBL. Ehr. Inf. ; Pritchard, Inf. ; 

 Williamson, Tr. Phil. Soc. Manchester, vol. 

 ix. ; Tr. MM. Soc. 2.i. 45 ; Busk, ibid. 31 ; 

 Cohn, Ann. So. Nat. 4. v. 323 ; Ann. N. H. 

 2. xix. 187 ; Rabenh. Alg. iii. 26 ; Cooke, 

 Alga, 1882. 



VORTICEL'LA, Linn. A genus of 

 Peritrichous Infusoria, of the family Vor- 

 ticellina. 



Char. Body campanulate, with an ante- 

 rior ring of cilia, stalked j stalk simple, spi- 

 rally contractile. 



These interesting Infusoria are very coni- 

 nionlv met with in decomposing vegetable 

 infusions, as of hay, portions of dead 

 flowers, &c. Their curious metamorphoses 

 and modes of reproduction, are noticed under 

 INFUSORIA. 



