I f
,
56
C h lam y d om o n a s p n lv is c u lu s . Ehr. Infus. p. 64i.
Macrogonidia ovate, twice as long as broad, or nearly ; deep
green, with a bright red lateral spot.
S i z e . Diam. -OoeS-'Olo mm.
Rabh. Alg. Eur. iii. 94. Cohn in Nova Acta. xxiv. t. 18, f.
28. Freseniiis Beitr. 235, t. 11, f. 43-45. Pritchard Infiis.
521, t. 18, f. 40, 51-54.
Diselmis viridis, Diijard. Zoopliy. 342 iii. f. 20, 21.
In stagnant water.
“ These creatures form a large portion of the green matter which
colours the water contained in water-butts, ponds, and puddles in the
summer and antnmn, especially after a storm. Whenever these exist in
large quantities, multitudes of them, and of their envelopes, rise to the
surface of the water, and form a green stratum upon it.”—Pritchard.
Plate X X I . fig. 3. a, swarmspore; h, c, encysted and undergoing
division ; d to g, glæocystis forms ; A, resting cells, after Cienkowski X
400 ; i, stellate cyst, from Stein ; j , individual differentiated ; k, swarming
X 600.
G en u s 39. VOL VOX. lA n n . (1758.)
Cænobinm sphærical, continually rotating and moving, looking
like a hollow globe, composed of very numerous cells
arranged on the periphery at regular distances, connected by
the matrical gelatin ; furnished with a red lateral spot, two
contractile vacuoles, and two long exserted cilia, all circumscribed
within a common hyaline vesicle. Propagation sexual
or non-sexual. In the non-sexual certain distant cells greatly
enlarge, divide into numerous parts, and evolve daughter-
coenobia within the parent-coenobia, which are ultimately set
free. In sexual propagation certain masculine cells undergo a
multipartite division into fascicles of mobile spermatozoids
which are contractile, pear-shaped, and biciliate, afterwards
free. The female cells are enlarged, bnt do not undergo
division ; after fertilization they develop into motionless
oospores, which are finally red, surrounded by a double epispore.
The following is a summary of the structure and life-history, of
Volvox as given by A. W. Wills in the “ Midland Naturalist”
(Sept.-Got., 1880)
“ I t seems hardly necessary to describe the normal aspect of this
organism. Briefly, under a low power, it is seen to consist of a sphærical
globe of mathematical perfectness, so transpart nt that, as it glides
along, any object over which it passes is clearly visible through its
vacant spaces, i.e., through such parts as are not occupied by the structures
presently to be noticed, while by focussing the binocular on the
|)t
lower half of the plant the effect is obtained of looking into the inside
of a glass sphere of crystalline purity and of absolute symmetry. The
diameter of a full-grown Volvox is usually about 1-60", and individuals
are to be found in each colony varying from this down to about 1-80”.
The inne7' surface of the sphere is studded at intervals with dark green
points, not disposed irregularly, but so arranged that each is usually the
centre of a group of six others, placed at the extremity of nearly equal
radii. These green points are ‘ gonidia,’ each probably endowed with
the potentiality of becoming a perfect Volvox, though only a certain
uumber of them actually undergo that sequence of changes which
results iu their becoming fresh individuals resembling the parent
sphere.
“ Each gonidium is either sphærical or pyriform (in w’hich case its
pointed end is directed outwards), and contains, in its early stages at
any rate, one or more contractile vacuoles disposed among a mass of
gi'anular endochrome, and stated by Busk to pulsate rhythmically once
in about forty seconds. (Plate 23, Pig. 6.)
“ At this period are also to be seen in the body of the gonidium one,
two, or three—occasionally even more—brilliant colourless spots, from
one of which is probably derived a nucleus which can be detected by the
use of reagents at a later period.
“ There is also often lodged within the substance of the zoospore a
brown or red ‘ eye-spot,’ and all the eye-spots in an individual look, so to
speak, one way.
“ The apex of each gonidium is more or less produced into a transparent
point, from which proceed two cilia several times as long as the
gonidium itself, which pass through two minute pores in the outer cell
wall, and move freely in the surrounding water. I am fortunate in
having mounted a specimen of Volvox, in which these pairs of foramina
are clearly shown, and the regularity of their disposition at a uniform
angle to the equator of the sphere is striking. (Plate 23, Fig. 7.) I t is,
of course, by the combined action of these numerous pairs of cilia that
the whole organism progresses. Of the direction of the resultant
motion we shall speak shortly.
“ Viewing the surface of the sphere with its convexity presented to
the objective, we find, by very careful adjustment of light, that from
each gonidium there runs to each of the six surrounding ones a fine
thread, sometimes double, occasionally triple, always of extreme tenuity
(Plate 22, Figs. 1 and 3), of svch tenuity, indeed, as to be frequently
invisible ; but as the use of certain reagents often brings these lines
into view where it had been previously impossible to detect them, and
as they may be sometimes discerned for an instant when the eye is
applied fresh and unfatigued to the microscope where even a moment
later they seem to be absent, it may be assumed that the structure is
universal, though often far too subtle to be detected. I t is needless to
say that no skill of the draughtsman can even suggest its infinite delicacy,
while the figures given in books, not excepting the beautiful
drawings in Ehrenberg’s * Infusionsthierchen,’ exaggerate the strength
of the connecting lines to the extent of grossly caricaturing the extreme
fineness of Nature’s own handiwork.
“ To return to the gonidia and their history. A certain number of
these in each individual are selected to produce a group of young Vol-
voces within the parent sphere. The books fix this number as usually
four or eight ; but out of twenty-five individuals now in the field of my
microscope I find only three containing four incipient spheres of the
second generation, while only one contains eight, and there are four
containing five, six with six, ten with seven, and one with nine such
progeny. Almost every Volvox, when first discharged from the parent