442 
MR. H. N. MOSELEY OR THE STRUCTURE OF THE STYLASTERID2E. 
way to the exterior. I have not had sufficient material at command to determine 
whether the ampullae, as they enlarge, come gradually to communicate with the 
surface of the corallum by means of absorption of the intervening hard tissues. It 
seems probable that they may do so. 
The ova /ire solitary, one only being developed in each growing ampulla. Each 
ovum is developed within the cup of a cup-shaped spadix (Plate 41, 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 fertilization takes place — that is to say, how the spermatozoa find then* way 
to the sometimes deeply-seated ova. As the ovum advances in development and 
increases in size, the spadix enlarges with it (Plate 41, fig. 2, G). Subsequently, how- 
ever, 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 (Plate 41, fig. 2, P) is a large object of an ovoid form, 
with a long diameter greater than the extreme width of the gastrozooids. 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 striae 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 ectodermal 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 planulse become folded to a slight extent, as in the 
case of those of Errina labiata (Plate 37), in order to accommodate their length within 
the ampullae. 
The male stocks of Pliobothrus symmetricus are in every way similar in structure to 
the female, with the exception that they bear male gonophores instead of female in 
their smaller ampullae. 
The male gonophores (Plate 41, fig. 3) are sacs containing a number of small ovoid 
bodies, which contain spermatozoa or sperm -cells in various stages of development. 
The exact structure of these smaller bodies, and of them relations to the endoderm, 
were not determined. 
(3.) GENUS ERRINA (GRAY). 
The genus Errina was formed by Gray to contain the Millepora aspera of Linnaeus 
and Esper. Gray gave a short diagnosis of the genus in the Proc. Zool. Soc., 1835, 
p. 85, from specimens in the British Museum ; and this was supplemented by Savile 
Kent, in a paper published in the same journal for 1871, p. 282, by further reference 
to the same specimens. A specimen dredged by H.M.S. ‘ Challenger ’ off the mouth 
of the Rio de la Plata in GOO fathoms, is clearly referable to this genus, but represents 
a new species, for which the name Errina labiata is adopted. 
