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Still more interesting is the statement about the parasitic occurrence of species of this
sub-genus that is given by Cn. B. WlLSON, 1913 (a preliminary note 1911, p. 22). This author
describes (p. 269) a new species called Gypridina parasitica, which is certainly unidentifiable
as a species, but without doubt belongs to the same sub-genus as does the species that I have
dealt with above. This form seems to have been discovered as a parasite in no less than five
cases: „Five lots of this o s t r a c o d were obtained in all; two of these were taken from the
gills of two hammer-head sharks, Sphyrna zygaena, on July 9, and include about 50 specimens
each . . . The third lot contains a single specimen founcl on the gills of Epinephelus adscensionis,
August 9. . . . The fourth lot contains three specimens taken from the gills of a jack, Caranx
crysos, August 1. The fifth lot contains 12 specimens and was obtained from the nasal tubes
of the hammer-head shark on June 17.“
Whether all these finds given by WlLSON really refer to a single species is anything but
certain, at least if we are to judge from the superficial way in which the species in question is
described and reproduced. A comparison between the two reproductions of the furca given
in pi. 53, figs. 303 and 311 is even decidedly against such an assumption.
On the same page on which this information is fo und WlLSON gives the folio wing details
about these finds. „That the presence of these ostracods on the fishes’ gills was not
accidentai is abundantly proven by the following considérations: First there were too many
of tliem; one or two or half a dozen might be washed on to the gills of a fish accidentally,
but not 40 or 50. Again they were arranged altogether too regularly; in the space between
the bases of two adjacent filaments and in contact with the gili arch, there was always a single
ostracod, its long diameter at right angles to the gili arch, so that its anterior end
projected slightly on one side between the filaments, and its posterior end on the other side. —
Furthermore the tissues of each filament where they came in contact with the shell of the
ostracod, were hollowed out in the center and slightly raised around the edges, thus forming
a sort of pocket, •which held the ostracod securely in place so that it could be removed
only with a pair of forceps. This of course is absolute proof that the ostracod was not
washed in temporarily, but that it had remained in position long enough to produce this effect
on the tissues. Tn view of such conditions these ostracods may fairly be called parasitic.
While it is impossible to see how they can draw any biood from the fish’s gills, yet they certainly
share the oxygenated water with which the fisli keeps its gills supplied, and they get their food
in some way while there. For food they may devour anything that the water contains and
brings to them, they may eat scraps of the fish’s food that come their way, or they may feed
on the slime with which the fish’s gills are covered. It is impossible to détermine at present
just what does constitute their diet.“
No adaptation for parasitism of one kind or the other can be disco vered in the
form in question — at least if we are to judge from WiLSON’s description and figures; on the
contrarv this species must be said to have the structure that is typical for free-living forms
of this genus. Accordingly it seems to me doubtful whether we are concerned in this case,
contrary to the two preceding ones, with a (or several) exclu sivel y parasitic form
or forms.
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