514 Harper .-—Cell-Division in Sporangia and Asci. 
cases the young spore is decidedly lobed as in b , Fig. 45. 
d , in the same section, shows the plasma-membrane of the 
young spore indented, as a result of some disturbance in 
fixation which also produced the vacuole-like space lying 
opposite the indentation. In Fig. 47 we have a section showing 
seven of the eight ascospores completely enclosed in plasma- 
membranes isolating them from the adjacent spore-plasm. 
They have come to lie now in a more nearly median row in 
the ascus, though a and b are still overlapping, and the eighth 
at the lower end of the series was almost wholly in the next 
section and was hence omitted from the drawing. The astral 
rays have disappeared, though in a, b , c, and f, the beak 
and central body have not yet been drawn back to the nucleus. 
The nuclei have increased considerably in diameter and the 
chromatin forms a regularly distributed network. The spores 
are flattened upon each other and maintain their individuality 
and rounded outlines, indicating the existence of surface 
tension in their plasma-membranes. No cell-wall is present 
as yet. 
As I have pointed out in my former paper the existence of 
surface tension in the spores at this stage is most conclusive 
evidence for the view that the plasma-membrane is a specially 
differentiated layer. As we have seen, the protoplasm of the 
ascus is entirely homogeneous before the spores are cut out by 
the metamorphosis of the aster, and to prevent the plasma in 
the spore from mixing and becoming continuous with the 
epiplasm outside, the assumption of the differentiation of 
a membrane-layer is essential. It is not necessarily implied 
that this differentiation is chemical ; it may consist perhaps 
in an increased density and absence of coarser granules. 
I am inclined however to consider a very decided differentia- 
tion as necessary, since it can hardly be seen how a merely 
denser, more homogeneous colloidal layer could fail to lose its 
identity and diffuse into a chemically similar compound on 
both of its surfaces. If it be assumed, as claimed by Rhumbler 
for Amoeba, that the ectosarc is formed from the endosarc as 
a result of contact with water, and that in the ascospore, as 
