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REPORT ON CORALS—HYDROCORALLIN AE. 49 
of an upper cylindrical portion (Pl. VIII. fig. 2, Z), and a wider saucer-shaped basal 
region, to join the margins of which the lower part of the cylindrical portion gradually 
widens out inferiorly. Canals are given off from the margin of the basal saucer of the 
zooid all round, and pass to join the general coenenchymal meshwork; but no canals 
at all are given off from the rounded under surface of the zooid. The upper surface of 
the cylindrical portion of the zooid is nearly flat, and is occupied by the mouth, which 
is a cruciform slit bounded by elongate gastric endoderm cells, closely similar to those 
described as existing in Sporadopora. 
The dactylozooids are simple elongate-conical bodies devoid of mouths, with a minute 
structure closely similar to that of the corresponding zooids of Sporadopora. In the 
retracted condition they are thrown into a series of transverse folds which are indicated 
by fine transverse lines in the figure (Pl. VIII. fig. 2, TZ, TZ). The zooids appear to 
be retracted directly within their sheath, and not to be attached on one side of their 
base. 
The gonophores are contained in ampulle, which are often sunk deep within the 
ceenosteum; and it is not apparent by what means the large mature planule find their way 
to the exterior. Ihave not had sufficient material at command to determine whether 
the ampulle, as they enlarge, come gradually to communicate with the surface of the 
coenosteum by means of absorption of the intervening hard tissues. It seems probable 
that they may do so. 
The ova are solitary, one only being developed in each growing ampulla. Each ovum 
is developed within the cup of a cup-shaped spadix (Pl. VIII. fig. 2, 0). The ovum is 
provided with a germinal vesicle and spot. It is covered by a fine layer of ectoderm, 
which is reflected over it from the surface of the spadix. It is not patent how fertili- 
sation takes place—that is to say, how the spermatozoa find their way to the sometimes 
deeply-seated ova. As the ovum advances in development and increases in size, the 
spadix enlarges with it (Pl. VIII. fig. 2,G). Subsequently, however, in later stages, 
the spadix appears not to increase further; and when in relation with a nearly fully- 
developed planula appears proportionately small. 
The nearly mature planula (Pl. VIII. fig. 2, P) is a large object of an ovoid form, 
with a long diameter greater than the extreme width of the gastrozooid. Its ectoderm 
and endoderm are plainly differentiated. The endoderm is composed mainly of oil-cells, 
but contains also a few fully formed nematocysts of the larger variety. The ectoderm, a 
thick layer, shows the characteristic striation vertical to the outer surface of the planula, 
the strie being composed of granules and nuclei arranged in linear groups. As far as 
could be ascertained from the scanty material at command, it appeared that the ectoder- 
mal layer is formed in development by the process of delamination. No trace of an 
invagination in the embryo was observed. 
In very advanced stages the planule become folded to a slight extent, as in the case 
(ZOOL, CHALL. EXP.—PART ViI.—1880.) G7 
