ON THE DEVELOPMENT OF LICHENOPORA VERRUCARIA. 89 
place; acu Bis the basal lamina. The zocecium whose point 
is marked p has its upper end free, even in the earlier con- 
dition, while that marked £ is still incomplete on its distal 
side (cf. fig. 14). It is soon completed on that side by an 
obliquely vertical septum, which starts at Fr; and the pro- 
longation of this septum forms the lower wall of the zocecium. 
By the time that the margin of the colony has extended to BI, 
the two radial septa, which at first formed the lateral parts of 
the zocecium £, have grown in length and in height; and they 
are supposed to have meanwhile given rise to the beginning of 
a new zocecium, G, which has reached the condition of & in 
the earlier phase. 
In examining the woodcut in the condition indicated by the 
dotted lines, it is clear that a space occurs between the two 
older zocecia, and a much younger one between the two younger 
zoecia. Smitt (20) alludes to a space of this nature as an 
“ interstitialrum ;” but it will be convenient to substitute the 
term “ alveolus.” 
The zocecia may be arranged in radial series, as shown in 
the woodcut; or their position may be for the most part 
alternate, as in fig. 14. The upper sides of the zocecia are 
marked with longitudinal ridges, which have been omitted 
from most of the figures for the sake of simplicity, but are 
shown in figs. 8 and 9. The projecting spikes of the zocecia 
are commonly continuous with these ridges, some of which 
become exaggerated at their lower ends to form lateral walls 
for the alveoli. These are thus pyramidal spaces, pointed at 
their lower ends, and at first only closed by membrane above. 
They increase in length by the growth of the zocecia, and by 
the extension of the vertical septa on sides where they are not 
bounded by zocecia. The septa do not, however, grow so high as 
the zocecia; but after they have reached a certain height, each 
alveolus commences to become roofed by the calcification of the 
membrane which is already present in that situation. The 
calcification of the roof of each alveolus begins at the margin 
and gradually advances to the centre, in the same way that an 
opening is gradually closed by the contraction of a sphincter 
