XXll 
INTRODUCTION. 
and maintained a connection between the zooecia and the tissues 
secreting the epizoarium, just as the ordinary interzooecial spaces 
were occupied by the soft tissues which cover the surface of the 
zoarium. Eut as the tubuli were spaces left in secondary calci- 
fications outside the zooecial cavities, they may be regarded as 
extra-zooecial in origin. 
The origin of round spaces or ‘ maculae ’ by the irregular 
thickening of the wall of the zoarium is shown in Tigs. 2 and 3. 
Eig. 2 is a diagram of the structure of Fetalopora after Pocta, and 
Eig. 3 shows the actual structure as seen in a thin section of 
Sparsicavea undulata ; in that species there are two or three 
maculae between adjacent peristomes, and they are formed as pits, 
left by the thickening of the outer wall. Some of the longer 
maculae are divided by a transverse tabula. A condition inter- 
mediate between the typical short maculae and the long tubuli is 
shown by some long and thin maculae in Sparsicavea undulata 
(Eig. 3), which approximate to the branched tubuli of SipJiodictyum 
gracile (Eig. 4). 
Fig. 3. — Sparsicavea undulata (Hag.). Fig. 4. — Siphodicty uni gracile, 
Longitudinal section ; X 7 ‘5. Longitudinal section through wall 
with maculic. 
As to the nature and classificatory value of cancelli, I have not 
seen reason for any serious change of opinion since I used that term 
in 1893, though I then cautiously defined cancelli in more general 
terms than are now necessary. Eut Mr. Waters is quite just in 
his suspicion as to a change of view regarding the cancellous nature 
of the Discoporellidae (Lichenoporidae of many authors). And upon 
that question I am still undecided. IS’o final opinion appears to me 
possible until there has been a complete revision of the miscellaneous 
assemblage of recent species included under the name of Biscoporella 
by Eusk and of Lichenopora by Waters. 
