VOLVOCINES. 57 
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 inner 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 
number of them actually undergo that sequence of changes which 
results in their becoming fresh individuals resembling the parent 
sphere. 
“Each gonidium is either spherical or pyriform (in which 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 
granular endochrome, and stated by Busk to pulsate rhythmically once 
in about forty seconds. (Plate 23, Fig. 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 trans- 
parent point, from which proceed two cilia several times as long as the 
gonidinum 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.) It 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 sweh 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 ig 
universal, though often far too subtle to be detected. It is needless to 
say that no skill of the draughtsman can even suggest its infinite deli- 
cacy, 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 Vole 
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 
