VOLVOCINE.E. 73 



coloured contents of the individual portions become drawn back towards 

 the periphery in centrifugal direction, a colourless plasma remaining 

 about the central point ; this disappears at first in the centre, a cavity ia 

 formed in the middle of the disc, and as this enlarges the eight portions 

 assume the form of a wreath, consisting of eight globular or ellipsoid 

 bodies in close contact, usually not exactly in one plane, owing to the 

 outer membrane not having expanded in proportion to the enlargement of 

 the plasma. The original cilia continue active, causing the motion of 

 the whole organism, until the eight portions are completely individualized, 

 and then their motion ceares. The separate parts of the plasma now form 

 eight independent but closely packed membraneless primordial cells. 

 shortly afterwards a delicate membrane common to them all is secreted 

 beneath the mother-cell membrane round the disc formed by the primordial 

 cells. This membrane is at first in contact, but afterwards becomes further 

 and further removed as it swells and tends to assume a globular form. By 

 the motion of the cilia the mother-cell membrane is thrown off, and the 

 young family escapes into the water. When the Chlamydococcus-like 

 unicellular Stephaiiosphcera has commenced its Division early in the 

 evening, the division into eight is perfected during the night, and early 

 in the morning the young family quits its cast off mother- cell membrane. 



In the course of the day the individual primordial cells and their 

 common investing membrane grow until the latter attains a diameter 

 of "01 to '048 mm. During this growth the shape of the primordial 

 cells is changed by the formation of various prolongations, but in the 

 course of the afternoon they again become round, and during the even- 

 ing division commences in them precisely similar to the process in the 

 unicellular Stephanosphcera. On the following morning we find eight 

 young families. It is calculated that in eight days, under favourable 

 circumstances, 16,777,216 families may be formed from one resting cell 

 of Stephanosph&ra. 



We have given but a barren outline of the history of this little plant, 

 but for further information must refer the student to Cohn's Original 

 Memoir in Siebold and Kolliker's Zeitschrift fur Zoologie, 1852, p. 

 77. Translated in the "Annals of Natural History," 2nd series. Vol. X., 

 pp. 321 and 401. Also Cohn and Wichura's subsequent memoir " Ueber 

 Stephanosphrera " in Nova Acta Acad. Leop. Car., 1857, part I., Vol. 

 XXVI. Of which an abstract is given by Currey in " Quarterly Journal 

 of Microscopical Science," Vol. VI. (1858), p. 131. Also an admirable 

 summary by Archer in the " Quart. Journ. of Microscopical Science " 

 for 1865, p. 117, with additional observations by himself. 



Plate XXV I II. jig. 1. Polar view of family with globose primordial 

 cells ; 2, equatorial view, with fusiform primordial cells ending in 

 mucous filaments ; 3, the same, with primordial cells collected on one 

 side ; 4, commencement of formation of macr ogonidia ; 5, all eight pri- 

 mordial cells divided in. fours ; 6, division advancing so that each 

 primordial cell consists of eight cuneate segments ; 7, further advanced 

 in division, movement in the mother-cell having commenced ; 8, 

 division completed, eight young individuals revolving in the mother- 

 cell ; 9, the eight original primordial cells broken up into mierogonidia j 

 10, young Stephanosphcera, (figs. 1 to 10 X 300) ; 11, mierogonidia after 

 exit from mother-cell X 500; 12, full-grown resting cells ; 13, commence- 

 ment of division in resting cell ; 14 to 19, successive stages in division 

 of resting cell ; 20 to 22, naked zoospores ; 23, 24, encysted zoospores ; 

 25 to 27, division of encysted zoospores ; 28, young eight-celled family 

 resulting from division of encysted zoospore ; 29, 30, young families, 

 all after Cohn X 400 ; 31, amaaboid condition of primordial cells, after 

 Archer. 



