35 2 
Burt. — The Development of 
Intermediate Stages. 
It is convenient to consider as young stages all those in 
which there is not yet any well-marked differentiation of the 
wall of the receptaculum ; as intermediate stages, those in 
which the wall of the receptaculum is present but not yet 
crowded into folds ; and as advanced stages those with the 
walls of the receptaculum folded. 
Sixth egg. — The rudiment of each part of the mature 
plant is now recognizable, occupying the position which it 
has in the old egg. This is apparent by a glance at Figs, io 
and 5. The latter, Fig. 5, represents a median longitudinal 
section through an egg about 2 mm. in diameter, drawn under 
lower magnification than the preceding figures. Comparing 
this with the general features of those figures, we observe, that 
the vigorous growth in the sheaf-like head N, which has gone 
on with its rapid differentiation, has greatly changed the 
relative proportions and apparent positions of the parts of 
those stages ; that the cortical layer C forms the outer 
covering of the egg, and is still present in greatest amount at 
its lower end ; and that the medullary bundle M runs upward 
through this basal mass to the lower end of the central column 
R. With the exception of the cortical layer C , and the 
medullary bundle M, all the rest of the egg has been found to 
arise from the sheaf-like head N. 
Examining the latter structure more closely, it may be seen 
that the central column R is now slightly contracted at its 
apex, and is taking on the slightly fusiform outline character- 
istic of the cavity of the stipe in the mature plant. Just 
outside the column R the rudiment of the wall of the stipe 
vS is becoming differentiated from the loose tissue A. Follow- 
ing Ed. Fischer, this loose tissue A will be called intermediate 
tissue (Zwischengeflecht\ but this term should not be used 
for the Clathreae. 
In later stages, splitting away of the volva from the gleba 
and receptaculum occurs through the zone i in a plane parallel 
with the outer surface of the egg. On the peripheral side of 
