120 ARCHER, ON STEPHANOSPHARA PLUVIALIS. 
attached to the inner surface of the envelope, but never per- 
forate it. When a Stephanosphera-globe is seen in polar 
view the outline of the primordial cells mostly appears 
somewhat acuminate towards the common envelope, and from 
such apex the pair of cilia take their origin. The primordial 
cells possess, immersed in their substance near the middle, 
two symmetrically-disposed, round bodies, called by Cohn 
nucleus-like vesicles, and said to possess an internal cavity.* 
To me, indeed, they appeared quite identical with the so- 
called *‘ chlorophyll-vesicles”’ (Nig.) of other plants, to which, 
indeed, Cohn afterwards compares them.+ Such may convey 
an idea of a perfect family—of a fully-grown Stephano- 
spheera. 
Now, as to the developmental changes connected with 
propagation, the primordial cells, as described by Cohn, 
undergo three kinds of changes. I shall first allude to that of 
“ macrospores.” The colourless prolongations of the primor- 
dial cells become drawn in, and the primordial cells them- 
selves become rounded. A slight elongation of a primordial 
cell about to vegetate then takes place; it becomes gradually 
transversely constricted and divided into two cells, which 
expand slightly from left to right; these two cells become 
divided each into two, those again ‘into tw o, thus producing 
eight; the constrictions, however, taking place only in such 
directions that the young resultant group presents the form 
of a flattened spheroid, having somewhat the appearance, 
when either of the larger surfaces is towards the observer, of a 
wheel. These changes do not take place simultaneously in all 
the eight primordial cells of an old sphere, but are to be met 
with in different degrees of advancement. The further 
growth consists m the development of a,delicate common 
membrane closely investing the young disc-like family, and in 
the centrifugal separation of the new primordial cells, upon the 
completion of the several radial constrictions, and in the de- 
velopment of cilia. After escape into the water by the 
bursting of the original envelope-cell the new envelope-cell 
of the young family, from being at first of a very considerably 
depressed figure, gradually expands in the polar direction 
until the spherical form is attained—the primordial cells 
meanwhile acquiring their mature appearance and structure. 
Thus, each parent Stephanosphera can normally give rise to 
eight young Stephanosphare, though families of but four 
* Loe. eit. ( Ucber cine neve Gattung aus der Familic der Volyocinen ”), 
G3 
FB) 
+ Ibid., p. 97. 
