[Fi
i.'t i f
a n d a lo n g th is p a s s a g e th e eggs, w h ic h a re r em a rk ab
ly la rg e , u pw a rd s o f a m illim e tr e in d iam e te r Avhen
th e y leaA'e th e OA'ary, a re passed, a n d a re a rra n g e d
A'ery re g u la r ly in roAA'S on th e floor o f th e p o u c h , each
eg g h e in g k e p t in its p la c e b y tAvo or th r e e sh o rt
sp in e s AA'liicb b en d over it (F ig . 46).
Among th e very many examples of this Ilemiastei'
J’ji;. 4{y.— l k m i a s k r y h ilip p ii. The arrangement of the eggs in one of the niarsiipial
recesses. Five times the natural size,
AA'hich Ave dredged in Accessible Bay, and afterwards
in Cascade Harbour, Kerguelen, there Avei-e young in
all stages in the breeding-pouclies ; and although from
the large size and the opacity of the egg and embryo it
is not a very favourable species for observation, had
otberconditionsbeenfavourablc, we had all the material
for Avorking out the earlier stages in the development of
the young very fully. The eggs, on heing first placed
in the pouches, are sph erical granular masses of a deep
orange colour, enclosed within a pliable vitelline
membrane, Avhich they entirely fill. They become
rapidly paler in colour hy the development of the
blastoderm ; they then increase in size probably hy
the imbibition of AA'ater into tbe gastrula caA'ity ; and
a whitish spot with a slightly raised border indicates
an opening Avhich, I liaA'e no reason to donht, is the
permanent month ; hut of this I cannot be absolutely
certain. The surface uoav assumes a translucent
appearance, and becomes deeply tinged Avith dark
purple and greenish pigment ; and almost immediately,
without any definite intermediate steps, the
outer wall is filled with calcified tissue, it becomes
covered Avith fine spines and pedicellariæ, a roAV of
tentacular feet come into action round the mouth, the
vent appears at the posterior extremity of the body,
and the young assumes nearly the form of the adult.
These later changes take place very quickly ; but they
are accompanied hy the production of so much heavy
purple and dark green pigment that it is difficult to
follow them. The viscera are produced at the expense
of the abundant yelk ; and the animals at once take
a great start in size by the imbibition of Avater into
the previsceral cavity. The young urchins jostle one
another on the floor of the hreeding-pouch, those
below pushing the others np until the upper set are
forced out between the roAVS of fringing spines of the
pouch; hut CA'cn hefore leaving the marsnpium, on
carefully opening the shell of the yonng, the intestine