Harper. — Cell-Division in Sporangia and Asci. 483 
in cleavage, since in many cases the grooves open as fast 
as they are formed, while in others they remain closed till 
a much later period (Fig. 4). The separation of the surfaces 
thus formed need not proceed from the periphery inward. 
Frequently furrows are found closed at the periphery and 
widely open deeper in the mass of the cell. The formation 
of the cleavage furrows is the essential process ; whether the 
surfaces thus formed separate earlier or later is a matter of 
secondary significance. That these cleavage lines are not 
long meridional furrows dividing the initial cell symmetrically, 
as is the case in the sea-urchin’s egg for example, is clearly 
seen from surface sections of cells in the first stages of 
segmentation, as shown in Fig. 5. We see here that the 
cleavage surfaces intersect each other at very varying angles, 
so as to mark off the surface of the cell by an irregular 
network of grooves in which the meshes are of very irregular 
shape and of unequal dimensions. The grooves seem to 
appear first, at least in some cases, on one hemisphere of 
the cell, and to spread gradually outward over the other. 
In other cases cleavage seems to begin almost simultaneously 
over the whole surface of the cell. In the first set of cases 
I endeavoured to determine whether cleavage began on the 
superficial or deeper surface of the cell, as it lies in the 
epidermis of the host, but I could discover no regularity in 
this respect. 
The cleavage is progressive from the surface inward, the 
furrows deepening in general in a radial direction. Still they 
may be curved, and are inclined to each other at very varying 
angles and frequently form intersections at points near the 
surface of the cell, thus cutting off superficial blocks of proto- 
plasm of varying shapes and sizes. Sometimes this tendency 
to cut off a superficial layer of segments is very marked (Fig. 
2), so that we have a central solid mass or cell of protoplasm 
surrounded by a layer of superficial cells ; in other cases 
the furrows grow radially inward without intersecting till 
near the centre, thus forming narrow cones and pyramids 
with their bases outward. As the process of cleavage goes 
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