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Aggregates of eosinophilic leucocytes, were present in 12.4% (16 of 129)
of the digestive glands examined. Almost all cases were in specimens
from Aber Wrac'h or Aber Benoit (Table 3). For the purpose of this study,
these were termed focal leucocytoses. They differed from a general leucocytosis
in that the leucocytes were in a dense clump, sometimes focal,
rather than being dispersed throughout the tissues. General leucocytosis
may possibly, in some cases, be a part of a focal inflammation viewed
some distance from the focal foreign body or parasite. Some cases of
focal leucocytosis appeared to be confined to the leydig tissue surrounding
the diverticulae and were not totally "focal". In most cases, however,
the condition involved mass invasion of the lumina by leucocytes and/or
phagocytes with large numbers of leucocytes and/or phagocytes massed in
the surrounding leydig tissue. Decomposed portions of copepods were
present in the lumina of two specimens and no doubt were responsible
for the mass inflammation. Copepods were not apparent in the leucocytic
inflammations in the digestive glands of the other specimens. These
inflammations, or focal leucocytoses, may also have been responses to
copepods as they were identical in all aspects except for the observed
presence of copepods in the section.
In one case, well-formed focal aggregates were present in the leydig
tissue adjacent to the digestive gland. In one, the leucocytes were confined
to a well-formed "pocket", while in another the leucocytes were
also spread from the "pocket" to adjacent leydig tissue. A massive
pocket of leucocytes was present in one of the digestive glands examined.
Leucocytes were confined to the large "pocket". Adjacent leydig cells
were compressed.
A degeneration of two or three diverticula was observed in one
digestive gland and was associated with a copepod parasite. This
involved a breakdown of the diverticular epithelia and basal membranes
with leucocytic inflammation.
Five (3.9%) of the samples examined bore small necrotic areas on
one to four diverticula. These areas were characterized by a breakdown
of cellular integrity accompanied by light staining cellular debris and
a limited number of leucocytes. Necrosis appeared to be minor.
Amoebae were present in the digestive gland of one C. gigas.
Digestive glands of 16 (12.4%) of the C. gigas examined contained
ciliates. Ciliates were evenly distributed among Aber Wrac'h, Aber
Benoit and Rade de Brest oysters and were sometimes quite numerous in
the diverticular lumina. Ciliates were oblong, with a somewhat pointed
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