ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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tentacles, about 100 in number, longitudinally striped, and about 72 
pairs of septa. The lip margin is much folded, and the gullet is very 
rudimentary. Where the complete septa of the first order are attached, 
the gullet is wrinkled like the leaves of “ greens.” Six pairs of prin- 
cipal septa, two directive, were observed ; the others occur, according to 
their size, in four orders. All bear reproductive organs, but there are 
no acontia. The body is surrounded with regular ridges and furrows, 
which run concentrically on the basal disc ; the wall has a median 
annular constriction ; circular muscles and marginal saccules are absent. 
This new genus is probably a specialised, simplified type of Hexactinia. 
Structure and Affinities of Heliopcra caerulea.* — Mr. G. C. 
Bourne has a memoir on the structure and the affinities of Heliopora 
cserulea , with some observations on the structure of Xenia and Heteroxenia. 
He directs attention to the recent figures of Heliopora given by Saville- 
Kent, who succeeded in seeing and figuring the expanded polyps, which 
Bourne and Moseley both failed to do. The tentacles in these figures 
are seen to be of the usual Alcyonarian type, that is pinnate. Curiously 
enough, Mr. Bourne has been unable to find any tra'-e of pinnae in any 
of his sections, and both in them and in Moseley’s figures and descrip- 
tions what may indicate the pinnae might equally be attributed to con- 
tractu n in spirit. 
When the corallum is decalcified soft tissues are seen to form a 
sheet covering the whole of the surface of the corallum, but penetrating a 
very little way into its interior. As the tissues on one face of the colony 
are not in any way connected with those on the opposite face, the axial part 
of the skeleton is destitute of living tissue. In the fully developed parts 
of the colony there is beneath the ectoderm a thin layer of mesogloea, which 
passes into the mesogloea of the polyps, and into that of the coenenchymal 
tubes. The general structure of the polyp is of the normal Alcyonarian 
type, and has been fully and accurately described by Moseley. The struc- 
tures known as coenenchymal caeca are peculiar to Heliopcra. The inner 
halves of the polyps are placed in direct communication with the adjacent 
coenenchymal cteca, and in indirect communication with oue another, by 
a network of canals which lies at the surface of the colony, and may be 
called the superficial canal system. The calcareous tissue is deposited 
by a special layer of cells, which completely invests the coenenchymal 
tubes, the inner halves of the polyps and inner parts of the superficial 
canals. As the superficial canals and the coenenchymal tubes are lined 
throughout by an endoderm, we find that the walls of these structures 
consist internally of a layer of endoderm, outside which is a thin layer 
of mesogloea, and outside this again, there is a layer of coral-producing 
cells, which Mr. Bourne calls caly coblasts. As to the nature of these 
cells, and the layer from which they are derived, Mr. Bourne adduces 
reasons for believing that they are ectodermic. Owing to the activity 
and division of the ectoderm, an ill-defined layer of some thickness is 
formed below it, whilst special cords of cells penetrate inwards beyond 
it, and become skeleton-producing cells or calycoblasts. 
A detailed account is given of the characters of the hard corallum, 
and a suggestion is made as to its growth and formation. In a flattened 
explanate frond there may be seen in vertical section a central cord, 
composed, as Mr. Bourne show.-, of numerous parallel vertical tubes, 
* Phil. Trans., clxxxvi. B (1895) pp. 455-83 (4 pis.). 
