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Gonium p e c to ra le . Mull. Ve7'mium,(p. 60.
Cænobinm flattened, quadrangular, composed of 16 green
cells, furnished with vibratile cilia.
S iz e . Cænobium, from -05 mm. Cells from -01 X ’007 mm.
Eabh. Alg. Eur. iii. 99. Müll. Anim. Inf. t. 16, f. 9 -H .
Ehrb. Infus. 56, t. 3, f. 1. Dujard. Zoophy. p. 318. Fooke
Studien, 30, t. 4, f. 7, 8. Fresen, Abhand. der Senck, p. 191,
t. 8. Cohn Nova Acta, xxiv. p. 169, t. 18, f. 9-27. P ritchard
Infus. p. 518.
In stagnant water.
The fullest aooount of Gonium is that by Cohn, published many years
ago, but nothing has been added to its history since. The following is a
summary of his observations • t. • u ■«;
Each family is invested with a colourless mucous sheath which is difficult
to be seen without adding some colouring matter to the water, as
there appears to he no tegument. Seen from above, it is a quadrilateral
tablet with rounded corners, or from the side elliptical. The primordial
cells are sixteen in number, four occupying the centre disposed
square, and three on each side external to these. The central cell of the
three on each side is seta little nearer towards the centre. The cells are
somewhat polygonal, the four central being hexagonal, and the twelve
external pentagonal. When young the angles can scarcely be distinguished.
This regular polygonal form indicates that each cell is surrounded
by a firm membrane, which retains them in a fixed form.
investing membrane may also be detected a t the angles of the cells, from
each of which it is extended in a short tubular process, which is quite
colourless. These processes are joined to those of contiguous cells, so
as to link them all together. These processes are not visible in immar
tnre families, being subsequently developed.
In other points the organization of the cells resembles Ohlamydomonas.
Their contents consist of protoplasm, coloured by chlorophyll, when old
containing numerous corpuscles, a central darker corpuscle, and often
several vacuoles. Each cell is furnished with two cilia, which proceed
from the protoplasm, through perforations in the cell wall.
The movements of the ooenobium resemble those of Stephatiosphcera ;
it revolves on its short axis, so that its polar aspect is that of a rotating
surface, whilst its equatorial is linear.
In the development by subdivision only the cell-oontents are concerned.
The fission takes place by four successive stages, or generations,
in each of which bisection of the cells oconrs, so that ultimately
each primordial cell is subdivided into sixteen portions. When the sub-
division is completed by the construction of these sixteen small cells,
they are seen to occupy the same position and arrangement in the
mother-cell as in the parent cænobinm.
The primordial cells of the newly formed coenobia appear uucouneoted
with each other. The movement of the parent ooenobium continues
until the last stage of fission is completed, when it ceases, and the
young daughter coenobia commence a movement within the parent cell,
sometimes appearing as a disc, and at others as a line, according as the
surface or the edge is turned towards the spectator.
At length the mother-cell ruptures, and the yonng colony escapes into
the water, moves about freely, and starts on an independent existence.
Supposing that a young Gonium after twenty-four hours is capable of
development by fission, it follows that, supposing the conditions favourable,
a single colony may on the second day develop 16, on the third
256, on the fourth 4,096, and at the end of the week 268,435,456 other
organisms like itself.
I t has been supposed that some of the cells become detached from the
mature ooenobium and pass iuto a resting condition, but this has not been
positively demonstrated, so that fissuration is the only mode of repro-
duotiou at present known.
A fuller abstract of this paper by Cohn (from “ Nova Acta,” Vol.
XXIV., p. 169; is given in Pritchard’s Infusoria (p. 153).
Plate X X V II. fig. 1. Gonium pectorale—a, b, c, families in different
positions X 400 ; d, e, the same, rather more highly magnified ; /, family
before division ; g, family of 16 cells divided into 16 daughter families ;
d to g after Stein.
Genus 43. S T E PH A N O S PH JE R A . Cohn. (l852.)
Cænobium throughout its whole life rotating and moving,
composed of 8 green cells, bearing two vibratile cilia, disposed
at equal distances around a circle, enclosed in a common
colourless hyaline, globose vesicle.
Propagation, both by macrogonidia arising from the eightfold
division of the green cells, bearing two cilia, with a lateral
red spot, congregated in families of eight ; and by microgonidia,
very much smaller, produced by multiplied division, at first revolving
within the common vesicle by the action of four cilia,
afterwards free, escaping singly.
S te p h a n o s p hæ ra p lu v i a l i s . Cohn Bedtvigia l.,p . 11.
Cells globose, elliptic or fusiform, often at each extremity
spreading out in mucous rays.
S iz e . Cænobium -026-’052 mm. Cells -006--012 mm.
Eabh. Alg. Eu r. iii. 100. Currey in Micr. Journ., 1858, vi.
p. 181, t. 6, f. 1 -2 7 . Cohn Zeitsohr. fur Wiss. ZooL, 1852,
iv. p. 77. ’Archer Micr. Journ., 1865, p. 116. Pritchard Inf.
p.’529, t. 19, f. 38-58.
In hollows of rooks, and in pools after rain.
Stephanospheera was first observed in 1850 in Germany, and since in
many places, including the British Isles. ^
I t consists of a hyaline globe, containing eight green primordial cells,
arranc^ed in a circle in its equator. The globe rotates upon an axis perpendicular
to the plane in which the primordial cells are arranged, and
moves actively in space by the aid of cilia, two of which proceed from
each of the primordial cells, and pierce the hyaline envelope, th e
primordial cells divide first into two, then four, and lastly into eight
portions ; these portions separate from each other in a tangential direction
thus forming a disc round which a cellular membrane is developed.
Two cilia are produced upon each segment, and thns eventually eight
yonng individuals are formed, which ultimately escape by fissure of the