PART I—ON THE HYDROCORALLIN A. 
INTRODUCTION. 
Tuts Part of the Report contains an account of the structure of Millepora nodosa, and 
a Monograph on the structure of the Sry_asTERIDA, together with a list of the species 
dredged by H.M.S. Challenger, and a further list of all species hitherto described. It 
is divided into three Sections, as follows :— 
Section [|.—Own THE STRUCTURE OF THE MILLEPORID®. 
Section [].—Own THE STRUCTURE OF THE STYLASTERID. 
Section I[].—GrneraL REMARKS ON THE HYDROCORALLIN®. 
It is mainly a reproduction of two papers on the structure of Hydroid Corals which were, 
by the permission of the Lords Commissioners of the Treasury, published as parts of a 
Preliminary Report on the results of the Challenger Expedition in the Philosophical 
Transactions of the Royal Society for 1877 and 1878." Certain alterations have, how- 
ever, been made in the account of the structure of Millepora, which were necessitated 
by the discovery, subsequent to the appearance of that paper, of the Hydroid nature of 
the StyLaAsTERIDz. The terms made use of have been altered where necessary in order to 
render them uniform throughout, and the whole has been revised and to a considerable — 
extent rearranged. The list of SryLastErtD& dredged by H.M.S. Challenger, with descrip- 
tions of a few new species, isa new addition. The zoological relations of the MILLEPoRIDa 
and of the STYLASTERID are discussed separately at the ends of the parts of the treatise 
relating to each of them, and a general discussion on the relations of the HypRocORALLIN& 
as a whole, and on their pedigree, concludes the Monograph. 
' On the Structure of a Species of Millepora occurring at Tahiti, Society Islands (Philosophical Transactions of 
the Royal Society, 1877, p. 117) ; The Croonian Lecture, On the Structure of the StyLasTeRIDa&, a family of Hydroid 
Stony Corals (ihid., 1878, p. 425). 
