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POPULAR SCIENCE REVIEW. 
assumed an orange colour, giving to the whole globule a red 
tinge. The vibratile cilia already described are arranged in 
pairs, each pair belonging to a separate peripheral corpuscle or 
cell. These peripheral cells contain each a green protoplasm- 
body, varying in shape according to the age of the individual, 
as shown in fig. 2, a, b ; they usually contain a minute starch- 
granule, a reddish-brown “ eye-spot,*’ analogous to that of swarm- 
cells (zoospores) and of the Flagellate Infusoria, and one or 
two contractile vacuoles, the cilia being borne at the narrow 
hyaline end. Each is surrounded by a gelatinous envelope, 
which is pierced by a number of canals, all lying nearly in one 
plane, and filled by green or colourless extensions of the proto- 
plasmic interior. Since the canals of adjoining cells correspond, 
the corpuscles appear as if connected together by a network of 
fine reticulations. The outer gelatinous wall of each cell is 
also perforated by two pores, through which the two vibratile 
cilia protrude into the surrounding water. They constitute a 
single peripheral layer enveloping the entire organism, corre- 
sponding to the plate which is characteristic of many Chroo- 
coccacese ; each one by itself would be undistinguishable from 
an ordinary swarm-cell of many filamentous Algae, or from the 
entire individual of Chlamyclococcus or Pleurococcus in its 
motile stage. They have, however, so far as is known, no 
reproductive function, and in this respect stand almost alone 
among cells endowed with a spontaneous power of motion. 
Besides these non-reproductive or sterile cells, there are in 
each Volvox-colony three kinds of reproductive cells — non- 
sexual (neuter), male, and female. The neuter reproductive cells, 
or parthenogonidia, as Cohn terms them, are similar in struc- 
ture to the sterile cells, but two or three times their size, i.e. 
from ’006 to *009 mm. in diameter. Very early in the develop- 
ment of the young colony, they begin to multiply by bipartition, 
and all the cells in the same colony or sphere are usually at one 
time in the same stage of development. This division has been 
followed by Cohn through four stages, as shown in fig. 3, cc-e, 
the fourth stage consisting of sixteen cells, beyond which he was 
unable to trace it, owing to the difficulty of the observation. At 
this stage it is described as having somewhat the form of a black- 
berry, each segment possessing a single chlorophyll-granule con- 
taining starch. The young colony is surrounded by a trans- 
parent membrane, which it at length breaks through, and carries 
on an independent existence within the cavity of the mother- 
colony, each of its cells developing a pair of cilia ; finally it 
escapes from its confinement in the mother-colony into the 
surrounding water. The normal number of parthenogonidia 
which thus develope into colonies within the mother-colony is 
eight, corresponding to the eight cells into which each of them 
