248 Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS 
in size which these chambers show, when compared with the small 
intercellular spaces in Fic. 10, is due to the vigorous growth of 
the bounding cells, accompanied by rapid cell divisions. At this 
stage the partitions show no evidence of outgrowths. Fic. 12 
represents the section just below the one shown in Fic. 11, the 
cells drawn, in part at least, forming the floors of the dorsal cham- 
bers. The figure shows many intercellular spaces, -which are 
clearly schizogenous in origin; these spaces represent the begin- 
nings of the more deeply situated chambers or, in some cases, the 
passageways leading from these chambers to the dorsal chambers. 
A longitudinal section, repre- 
senting about the same stages as 
those shown in Fics. 11 and 12, 
may be seen in Fic. 13, the left- 
hand side of the figure being 
toward the apical cell. The very 
rapid development of the cham- 
bers is clearly indicated, and light 
is thrown on the way in which 
the deeper chambers originate, 
such chambers being indicated by 
the letters a—e. It will be seen 
that some of these chambers 
seem to be completely enclosed, 
showing that they may have originated by a splitting of cell walls 
in compact tissue, and that others already communicate with 
more dorsally situated chambers. Whether the connecting 
passageways are always formed subsequently to the chambers, 
or whether the formation of the passageways may sometimes 
precede that of the chambers is not altogether clear. If the older, 
right-hand side of the figure is compared with the younger, left- 
hand side, it becomes evident that the tissue with intercellular 
spaces has almost tripled in thickness and that the dorsal chambers 
have become distinctly deeper. The rapid growth involved in 
these changes has taken place in the original partitions of the 
dorsal chambers, in the cells which formed their irregular floors 
and in the cells immediately beneath. As the writer conceives 
the process, the growth of the partitions is both horizontal and 
Fic. 13. Longitudinal section through 
young chambers, 500. a-ée, more 
deeply situated chambers. 
