THE ORGANIC CELL 
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pair forms a compound cell or zygote, around which an envelope 
is formed, and from which a new colony of sixteen or thirty-two 
cells develops. 
There is yet a third stage in the process of differentiation 
of the uniting reproductive cell, and this is beautifully illus- 
trated in the case of Volvox globator. Volvox consists of a 
hollow spherical colony, the cells being arranged in a single 
layer, and being connected together by cytoplasmic processes. 
As the time for reproduction approaches, the most profound 
changes take place in some of the cells. Some increase to a 
great size, and contain in their substance stored-up food 
material ; these enlarged cells become the egg-cells. Other 
cells divide into masses of very minute antherozoids. The 
rest of the cells of Volvox remain in a state of inactivity, and 
finally die. At this moment it is well to note that the cells 
forming the Volvox colony become differentiated into two 
great classes : (1) somatic- or body-cells ; and (2) reproductive- 
or germ-cells : this early foreshadowing of a differentiation 
into body- and germ-cells in Volvox persists, as we have already 
seen, in a more elaborate and accentuated form in all the 
multicellular plants and animals. 
To return to the fate of the antherozoids and oospheres. 
One antherozoid fuses with a single oosphere, and the resulting 
compound cell or zygote develops at a later date into a fresh 
colony. 
brane disappeared, mantle-fibres forming, and attaching themselves to the 
chromosomes. 
Metaphase and Anaphases op Mitosis in Spermatocytes of the Sala- 
mand er. (Driiner . ) 
E. Metaphase. The central spindle-fibres pass from pole to pole of the 
spindle. Outside them a thin layer of mantle-fibres attached to the divided 
chromosomes, of which only two are shown. Centrosomes and asters well 
seen. F. Transverse section through the mitotic figure, showing the ring of 
chromosomes surrounding the central spindle, the cut fibres of the spindle 
showing as dots. G. Anaphase, divergence of the daughter-chromosomes, 
exposing the central spindle. H. Later anaphase. Central spindle fully 
exposed ; mantle-fibres attached to the chromosomes. The cell now divides 
immediately — see next figure. 
Final Phases of Mitosis in Salamander Cells. (Flemming.) 
I. Chromosomes at the poles of the spindle, the body of the cell dividing. 
J. Cell immediately after division ; daughter nuclei re-forming, a centrosome 
just outside of each. The central granule is the mid-body. 
