158 BROOKLYN BOTANIC GARDEN MEMOIRS 
all its dimensions. It results rather in a characteristic elongation in 
one axis of the cell, the axes of elongation of the four cells tending to 
be tangential to the general outline of the four-celled group. Klein 
figures this elongation of the cells very clearly for Eudorina in the 
four- and again in the eight-celled stage (’88, Taf. VI, Fig. 61, 63). 
Overton shows it more crudely (89, Taf. II, Fig. 10) and I have been 
able to photograph it for one of the four cells (Fig. 4, Pl. II). It may 
take place successively rather than simultaneously in the four cells and 
apparently proceeds in either direction around the group. Biitschli’s 
figure (’83, Taf. XIV, 1 g.) shows rather crudely the resulting arrange- 
ment of the cells just after the third division. The division seems to 
be nearly simultaneous in all four cells and the wheel-formed group of 
eight results. This characteristic growth and elongation of the cells 
at this stage leads naturally to the oft-noted fact that the plane of the 
third division cuts that of the second obliquely rather than at right 
angles. A determining factor is, however, obviously the tendency to 
bisect the elongated cell at right angles to its major axis as well as 
the direct relation between the second and third cleavage planes. The 
elongation of the cells during division reminds one at once of the 
familiar elongation of the egg cell and other free globular cells at the 
time when the bipolar karyokinetic spindle figure is at its climax of 
development. We have no good figures of karyokinetic division in 
Volvox but Overton’s figure from a 200-celled colony (89, Taf. III, 18) 
shows telophase stages with the cells all elongated and the spindles 
in every case in the long axes of the cells. 
It seems obvious that such a cell form in division implies a spindle 
figure with polar asters and justifies the assumption that the same 
internal forces are operating in the elongation of the Volvox cell as in 
the dividing egg. Typical polar asters may be expected to be found 
at such a stage as that shown in Overton’s figure, like those shown by 
Swingle (97) for a corresponding stage of division in Sphacelaria. 
We may conclude then that the adhesion of the four mother cells 
makes it necessary that the movement of material preparatory to 
the production of two equivalent rounded daughter cells should take 
place upon their free surfaces and the result is the characteristic 
bulging and elongation of the four cells during division. That this 
change of form is associated with the production of the karyokinetic 
figure with two polar asters seems clear from the figures of division 
in other alga cells with centrosomes. In any one of the cells of the four- 
celled group (Fig. 3, Pl. II), for example, if the third spindle figure has 
its axis 90° from that of the second division and in the same plane it is 
obvious that one of the asters will not have space for its full expression 
and if the adhesion of the quadrants is strong the yielding will be on 
