382 
MUSCINEm. 
mella. The intercellular space is traversed by rows of cells which stretch across from 
the wall of the theca to the inner mass of tissue ; they resemble most nearly proto- 
nemal filaments, or those of Algae, but have been formed by simple differentiation of the 
tissue of the theca. They contain chlorophyll-granules like the inner cell-layers of 
the wall. The outer layer of the wall of the theca is developed into a very character- 
istic epidermis strongly cuticularised externally. The third or fourth layer of cells of the 
inner mass of tissue, which is therefore separated from the annular air-cavity by two or 
three layers of cells (forming the spore-sac), produces the mother-cells of the spores. 
The cells of this layer are first of all distinguished by being densely filled with proto- 
FlG. 268. — Piiiiaria hyg7-0}netrica ; 
transverse section through the spore- 
sac ; A, sit the primary mother-cells ; 
B, sm the spore-mother-cells not yet 
isolated ; a outer side, i inner side of 
the spore-sac (x 550). 
Fui. 269. — Development of the spores of Funaria hygrometrica observed in 
very dilute glycerine ; A mother-cells, at a still united, at b and c the separation has 
commenced; ^isolated mother-cells clothed with cell-walls; at /"expelling the 
protoplasmic contents ; C mother-cells with indication of the commencement of 
the bipartition of the contents ; D the contents have divided into four masses of 
protoplasm, still surrounded by the primary cell-wall, but they themselves are 
naked ; E the spores enveloped by cell-walls ; F ripe spores (X 550). 
Fig. 270.— Various states of division of the mother-cells of the spores oiFtcnaria 
hygrometrica, observed in water, the progress of development indicated by the 
letters a — i. 
plasm, in which lies a large central nucleus, and are attached without interstices to the 
surrounding tissue in a parenchymatous manner. From their division proceed the spore- 
mother-cells, which become isolated by the deliquescence of the cell-walls, and then float 
in the fluid contained in the spore-sac, till they form the spores by repeated division. 
The Spore-sac is the term given to those layers of cells by which the large air-cavity is 
separated from the spore-mother-cells. It seems convenient to consider the layers 
which bound the spore-cavity on the axial side (Fig. 268, i) also as a part of the 
spore-sac; its cells contain on both sides starch-forming chlorophyll-granules. The 
inner large-cefled tissue, which contains but little chlorophyll, and is thus surrounded 
