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POPULAR SCIENCE REVIEW. 
vent is seen on a small projecting papilla in the centre of the 
floor, and between the supporting ossicles of the valves five dark 
open arches lead into the spaces opposite the re-entering angles 
of the arms, which receive the ducts of the ovaries.” Although 
there is no doubt that this remarkable apparatus is destined for 
the reception of the eggs and the protection of the young 
during their development, the eggs having been found beneath 
the membrane in the angles of the arms, and, in a more 
advanced stage, under the central tent, the phenomena of 
development could not be studied, such delicate objects being 
always more or less destroyed when brought up from such great 
depths as that at which the Hymenaster was dredged. 
The last species noticed by Sir Wyville Thomson is a brittle 
star, or Ophiurid, named by him Ophiocoma didelphys. It was 
obtained in January, 1874, at the entrance to Royal Sound and 
in several of the fjords and bays of Kerguelen’s Land. The species 
is particularly remarkable for the number of its arms, which is 
normally seven, instead of five, and varies from six to nine. 
Most of the adult females of this Ophiocoma were found to 
have groups of young clinging to the upper surface of the disc, 
the largest being about one-fourth the size of the mother, and 
the others diminishing in size until the smallest were less than 
one-sixteenth of an inch across the disc. The largest of the 
young starfish were always uppermost, and their size decreased 
downwards, their starting point being the genital clefts on the 
lower surface of the mother’s body. The earlier stages appear 
to be passed through in the interbrachial parts of the body- 
cavity, in which, in many specimens, groups of eggs and of 
young in course of development were found. The examination 
of these proved that in this species the development of the 
young from the egg is perfectly direct, — no provisional mouth 
and no pseudembryonic appendages are found, and the primary 
aperture of the gastrula persists as the mouth and excretory 
orifice of the mature form. 
Although, as has already been stated, the production of a 
Pluteus or other pseudembryonic form, or of larvae with pro- 
visional appendages to be afterwards cast off, as a first stage of 
development is by no means universal among the Echinoder- 
mata, it is at least so general as to render the occurrence of 
these numerous instances of probably direct development in 
southern forms of the sub-kingdom extremely interesting. And 
it acquires a special interest from its being coupled with the 
possession by the adult of special arrangements (brood-cavities 
and nurseries) for the protection of the young. Of course, 
although the term tc marsupium ” has been applied by Sars and 
other writers to the brood-cavity in which the young Echinoderms 
are reared, the analogy with the true marsupial pouch of the lower 
