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lateral nuclei were present. The ciliates apparently provoked an
inflammatory response as most were surrounded by eosinophilic leucocytes
in the water tubules, or the surrounding tissues contained
abnormally high numbers of lucocytes.
One specimen contained the plasmodial stage of a sporozoan. Multinucleate
Plasmodia were subspherical to ovate. Numerous plasmodia were
dispersed throughout the gill, but most heavily in the leydig tissue of
the interlamellar area.
A single copepod was found on a gill filament of one C. gigas.
No necrotic areas were observed on the gills examined and the outer
columnar epithelium of the specimens examined appeared healthy. The
number of mucous glands in sections of randomly selected plica and terminal
grooves were counted in an effort to determine if specimens from
Aber Wrac'h and Aber Benoit contained more active glands than those from
Rade de Brest and lie Tudy. The results were inconclusive. The number
of mucus cells per unit area of gill was not statistically significantly
different among the three populations.
6. Mantle . - Sections of mantle from 130 specimens were examined.
Two or three pieces of mantle were dissected from specimens and oriented
to give a transverse section across the tri-lobed edge.
Histopathologies were noted in the mantle of 31.5% (41 of 130) of
the specimens examined. There were a total of 47 of the three pathology
types described below. The distribution of the pathologies among sampling
sites was nearly equal.
Abnormally high numbers of eosinophilic leucocytes were noted in
35.4% (46 of 130) of the specimens examined. Thirty-eight of the incidences
involved large numbers of leucocytes dispersed beneath the epithelium
or in the leydig tissue. Eight cases, however, involved leucocytes
which were more aggregated in clusters.
Sporozoans were found in the mantle of a single specimen.
No necrotic areas were found on any of the mantles examined. All
epithelial cells appeared healthy. In an effort to determine if the
mantle epithelium of oysters from Aber Wrac'h and Aber Benoit contained
significantly more mucous cells than specimens from Rade de Brest and
lie Tudy, the number of mucous cells in a high power field were counted
at a level even with the circumpallial nerve and an area three fields
higher. Specimens from Aber Wrac'h contained slightly more (average of
27.5 to 34 for the five collections) mucous cells than those from Aber
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