346 CHARLES LincoLn EDWARDS, 
in number from a very few and scattered to many and densely 
crowded. Of the remaining adults 7 have spicules only in the walls 
of the pedicels and tentacles, and 6 others have only the multiple 
end-plates in the pedicels but with abundant typical tentacle spieules. 
9 specimens (20°,), 8 adult and 1 young, do not seem to have 
spieules in the body-wall and pedicels, but 3 of these have a few, 
and 1, many spicules in the tentacles. Where the spicules are not 
present, in many cases, especially in the walls of the pedicels, the 
spaces from which these calcareous structures have been dissolved 
are clearly seen. It might be thought that the spicules had been 
dissolved by acid alcohol. However in all but 4 of the 46 specimens 
here considered this cannot be the case because of the presence of 
spicules, at least in the tentacles. Of the 3 remaining specimens, 
1 was preserved in the same jar with individuals having numerous 
spicules, hence we may safely conclude the dissolution of spicules 
to have been during the life of the holothurids. 
Usually the spicules are relatively much more abundant in the 
young of Oucumaria frondosa and are often densely crowded. With 
advancing age, and possibly under changes in the physiological 
condition of the individual at present unknown, the spicules are 
dissolved first in the body-wall, then in the walls of the pedicels, 
until only their end-plates persist, and finally in the tentacles. 
There is not, in this species, a series of degenerative changes 
analogous to those described for Stichopus japonica by Mırsukurı, 1897. 
In Oucumaria frondosa it is simply a question of the presence, or 
absence, of the spicules in certain parts, or the whole, of the specimen. 
ÖSTERGREN, 1896, showed that the young of Mesothuria intestinalis 
(AscaAn.) have many tables like those of Mesothuria multipes LUDwiG 
while in the adult such tables occur but rarely. The same author, 
1898, demonstrates that Holothuria aphanes LAMPERT is the young 
stage of Holothuria impatiens (Forsk.). The smaller, and slightly 
different, spicules of the former are dissolved and after a period 
with none of these calcareous particles present, the larger tables 
and buckles of Holothuria impatiens appear. HEROUARD, 1889, says 
that in Thyone subvillosa the spicules are more complicated in the 
young than the large majority of them are in the adult, and 
that in some species they disappear entirely. 
Polian vesicle. — Of the 79 specimens examined all have 
the mode of one Polian vesicle in the left dorsalinter-radius. 
Five of these speeimens have two vesicles; three with one additional 
