31 
[Fewkes. 
represented by deposits nor rich in the number of forms evolved, 
two deficiencies that in Europe mark what have been called resid- 
ual faunas. 
ON A NEW PARASITE OF AMPHIURA. 
BY J. WALTER FEWKES. 
The Secretary read a communication on the parasitism of a 
Crustacean in the brood cavities of a common brittle-star, Am- 
phiura squamata , which he had discovered while at work in the 
Marine Laboratory at Newport. 
The Ophiurans, or brittle-stars, have two methods of develop- 
ment or metamorphosis, known as the direct and indirect. In the 
indirect, the young passes through a stage called the pluteus in 
which a provisional organism is developed from which the young 
form by budding, the provisional organism, or pluteus, being event- 
ually absorbed by the growing young of the brittle-star. Our com- 
mon Ophiopholis, 0. aculeata, has such a pluteus. In the case of 
other Ophiurans as Amphiura, however, there is no free pluteus in 
their metamorphosis, but the young are developed, without no- 
madic stages, in special sacs of the mother, called brood-sacs, of 
which there are ten situated in pairs on each side of the arms. 
The young Amphiura passes its early life in these sacs, at first at- 
tached by an umbilicus, afterwards free, and remains there until it 
has reached a considerable size. Morphologically, both forms of 
metamorphosis are identical, but while certain structures, as for 
instance, parts of the calcareous framework of the pluteus, are rec- 
ognizable, a nomadic pluteus is never formed in this genus. 
In collecting adult Amphiurans in order to discover new stages 
in the development of the young, my attention was often attracted 
to certain adults of this genus in which a portion of the upper 
(aboral) surface of the body has a reddish color, while in most spec- 
imens the body is chocolate brown. This coloration was noticed 
to be ordinarily limited to a marginal region of the body just be- 
tween the radial shields. 
It was invariably found, when those adult Amphiurse with red- 
dish coloration on the aboral surface of the body were dissected, 
that young were absent from the brood-sacs. It was, moreover, al- 
most invariably found that in these adults the ovary had suffered 
a change and had degenerated into an amorphous mass in which 
