XX 
INTKODUCTION. 
as normal members of the colony rendered impossible ; but they 
might be revived as reproductive zooids and discharge their 
products into the chamber of the gonocyst. Dr. Harmer has 
shown that large compound ovicells are probably formed of several 
zooecia, for he remarks {op. cit. p. 137), “in the cases where 
two or more zooecia become fertile, the ovicell may be regarded 
as being composed of as many original zooecia.” 
Dr. Harmer’s work, therefore, appears fully to justify the 
distinction between gonoecia and gonocysts, and to support the 
view that several zooecia may help in the formation of a large 
gonocyst. 
Epizoaeidm. — This teiTu is adopted for that epizoarial layer for 
which the term epitheca has been borrowed from the descriptive 
nomenclature of corals. This layer to some extent corresponds to 
the epitheca of corals, but is more important and varied in its 
functions ; and as there is no theca in Bryozoa, the term epitheca 
is inappropriate. [The term ‘ epizoarial ’ was suggested in Yol. I. 
p. 129, but ‘ epithecal’ was then retained.] 
Caxcelli. — Spaces of interzooecial origin which remain either as 
simple or branched tubuli, or as maculae, round spots or spaces, in 
the walls of the zooecia. 
The term ‘ cancellus ’ has been variously used. Thus both 
H. A. Mcholson and Busk regarded cancelli as aborted zooecia in 
dimorphic zoaria, for which structures I have adopted Ulrich’s 
term ‘ mesopores.’ Smitt, Mr. Waters, and Dr. Harmer, on the 
other hand, regarded cancelli as derived from interzooecial spaces. 
Mr. Waters^ has devoted a couple of pages of his report on the 
Belgian Antarctic Expedition’s Bryozoa to comment on what he 
regards as the inconsistency between my use of the term cancelli 
in 1893 and 1896. He, however, compares a difference of two books 
published at a three years’ interval, while he himself made greater 
changes in the use of ‘ cancelli ’ in two papers published three 
months apart (cf. pp. xxxiii, xxxiv). 
The changes between my Catalogues of 1893 and 1896, moreover, 
are more apparent than real. Mr. Waters i*emarks that I used 
‘cancelli’ as a zoarial character in 1893 and as zooecial in 1896. 
1 A. W. Waters. Bryozoa: Expedition Antarctique Beige — Besultats du 
Voyage du S.Y. Belgica en 1897-9 : Zoologie, 1904, pp. 95, 96. 
