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 leuco- 

 cytosis 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 surround- 

 ing 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 con- 

 fined 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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