VOLVOX. 



[ 813 ] 



VOLVOX. 



See SPONDYLOMORUM and SYCAMINA. 

 BIBL. See the genera. 

 VOLVOX, L. A genus of Volvocinese 

 (Confervoid Algae), of which only one spe- 

 cies, V. globator (PI. 7. fig. 24), seems satis- 

 factorily established. This organism, occur- 

 ring not uncommonly and often in great 

 abundance in clear pools on open commons, 

 &c., appears to the naked eye as a minute 

 pale-green globule gently moving about in 

 the water ; its dimensions variable, but gene- 

 rally about 1-50" when full-grown. When 

 placed under a low magnifying power, it is 

 found to be a spherical membranous sac or 

 coenobium, studded all over with green points, 

 the entire body rolling over in the water 

 with a motion which is readily discerned to 

 be caused by innumerable cilia arranged 

 upon the surface of the globe. In the inte- 

 rior of the sac are generally seen dense 

 globes, in summer mostly of a green colour 

 (PL 7. fig. 24) : sometimes the cavity is 

 wholly filled up by a number of membranous 

 sacs exactly resembling the parent but de- 

 formed by mutual pressure (PI. 7. fig. 25) ; 

 and inside these are seen smaller green 

 bodies as in the former case. The cceno- 

 biurn is also flexible, yielding to pressure 

 and recovering its form, and in full-grown 

 specimens is generally ruptured at one point, 

 where the internal bodies escape, so that 

 the number varies; usually, however, the 

 original number is eight. 



The application of higher powers is requi- 

 site to discover the intimate structure of 

 Volvox, which, by the researches of Wil- 

 liamson and Busk, most of whose observa- 

 tions we have verified, has been pretty 

 clearly made out. The outer envelope con- 

 sists of a layer of cell-membrane, in all 

 probability composed of a modification of 

 cellulose, although we have never succeeded 

 in producing more than a faint purple tinge 

 with sulphuric acid and iodine. By the 

 application of a sufficient magnifying power, 

 the green corpuscles at the periphery are 

 found to consist of zoospore-like bodies (go- 

 nidia, PI. 7. fig. 28), which are seated inside 

 the membranous envelope, each sending out 

 its pair of vibratile cilia (figs. 24-30) through 

 separate orifices in the external coat. The 

 same investigation will reveal that the 

 green gonidia have radiating processes ex- 

 tending from their sides, and running from 

 the different centres to meet each other in 

 the light interspace, forming thus a kind of 

 delicate network beneath the membrane. 

 The gonidia are pyriform, have a transpa- 



rent anterior end bearing a pair of cilia, 

 and contain a reddish-brown eye-spot and 

 a contractile vacuole, thus exactly resembling 

 those of Gonium, and indeed the zoospores 

 of Confervoids generally. The radiating 

 processes resemble those found in particular 

 stages of PROTOCOCCUS pluvialis, running 

 through the gelatinous coat, and probably 

 may be compared to the radiating fila- 

 ments proceeding from the nucleus of SPI- 

 ROGYRA (PI. 9. fig. 26). There is somewhat 

 more difficulty in determining the nature of 

 the structure in which the gonidia are en- 

 closed. There is a layer of soft consistence 

 of some thickness within the external mem- 

 brane; the green gonidia are wholly im- 

 bedded in this ; and their radiating processes 

 and cilia traverse the substance of it. We 

 are inclined to believe that this presents a 

 firm membranous layer again at the internal 

 surface, looking toward the general cavity 

 of the sphere. The nature of the soft layer 

 has been the subject of discussion ; we be- 

 lieve Busk's view to be correct, that it is 

 not formed by the collocation of distinct 

 membranous cells, like those of ordinary 

 parenchymatous structures, but by the close 

 juxtaposition of gelatinous envelopes of the 

 individual green bodies, resembling those 

 of Coccochloris, Glceocapsa, &c. We could 

 never detect a true line of demarcation 

 halfway between neighbouring gonidia : 

 an appearance is indeed sometimes pre- 

 sented in preparations kept in chloride 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. 7. fig. 30), the furrows 

 between which in certain foci give the ap- 

 pearance of a septum running round each 

 corpuscle (PL 7. fig. 29). Similar prepara- 

 tions also often show the gonidium con- 

 tracted and leaving an empty ring round 

 it, separating it from the gelatinous coat, 

 w 7 hicn runs undistinguishably into those of 

 the neighbouring gonidia. But the strongest 

 fact we have observed is that, by the appli- 

 cation of solution of potash, the substance 

 surrounding the gonidia is so entirely dis- 

 solved 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 gonidia and 

 their radiating processes intact, or at least 

 only shrunk and discoloured. If a true cell- 

 membrane existed around each gonidium, 



