ARCIIEE — ON STEPHANOSPHiEIlA PLT7VIALIS (C0Hn). 153 



Stephanosphaera-globe. Eegarding the direction of the wreath or series 

 of eight primordial cells as the equator of the globe, the rotating move- 

 ment is effected round the axis uniting its poles, and its vigorous onward 

 movement takes place in all possible directions. 



Scarcely a more charming spectacle can be than a multitude of these 

 elegant organisms vigorously rotating hither and thither, brightly green, 

 and, under a peculiar light, glittering and flashing as they move, now 

 showing a polar, now an equatorial view, or all intervening positions, 

 rapidly passing and repassing, curving, and wheeling, and gyrating, 

 crossing and recrossing each other, huddling and thronging sometimes 

 in numbers together, again starting off, occasionally rotating without 

 advancing or " resting on their oars," — some larger and older, some 

 smaller and younger, some' showing young revolving Stephanospheeree 

 within, some developing " microgonidia," — some in one stage, some in 

 another. In respect of beauty and gracefulness, indeed, a number of the 

 larger gently revolving emerald- studded globes of Volvox glolator, exe- 

 cuting their elegant revolutions, must, I think, carry off the palm ; but 

 their numbers, and the amazing energy of the gyrations of Stephano- 

 sphaera, the remarkable figure of the primordial cells, the differing sizes 

 and curious appearances of the variously developed globes might cause 

 some to give the latter the preference as a handsome object. Each, in- 

 deed, is certainly a charming sight ! 



To revert, however, to our subject. Notwithstanding that the struc- 

 ture and development of this organism have been copiously detailed in 

 Cohn's cited elaborate memoirs, a brief resume here will be necessary, 

 in order to draw particular attention by and by to one or two points 

 in its structure and organization, which I am disposed to think in 

 some measure foreshadow the remarkable phase presently to be ad- 

 verted to. 



Stephanosphocra then consists, as we have seen, of a family or colony 

 of eight green biciliated protoplasm-masses (primordial-cells), destitute of 

 a proper cell-membrane, and arranged in a circle, more or less approxi- 

 mately and at even distances from one another, at the equator of a 

 common enveloping hyaline rigid membranous sphere, composed of 

 cellulose, — the "envelope-cell" (" Hullzelle," Cohn). Though the 

 normal form of the envelope-cell is spherical, I have occasionally but 

 extremely rarely noticed such as possess, even when fully-grown, an 

 elliptic, or ovate, or sub triangular, or sometimes even a figure-of-8 

 shape : such very rare and casual distortions do not seem at all to inter- 

 fere with the otherwise normal growth and movements. 



It is by the action in the surrounding water of the two flagelliform 

 cilia belonging to each primordial cell, protruded directly through the 

 envelope-cell, that the revolving and onward movement of the total or- 

 ganism is effected. The primordial cells present great variety of form — 

 in the simplest condition globular, or nearly so. But in a fully grown 

 Stephanospha?ra when viewed cquatorially, these primordial cells very frc- 



