lateral nuclei were present. The ciliates apparently provoked an 

 inflammatory response as most were surrounded by eosinophilic leuco- 

 cytes in the water tubules, or the surrounding tissues contained 

 abnormally high numbers of lucocytes. 



One specimen contained the plasmodial stage of a sporozoan. Multi- 

 nucleate 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 term- 

 inal 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 inci- 

 dences involved large numbers of leucocytes dispersed beneath the epi- 

 thelium or in the leydig tissue. Eight cases, however, involved leuco- 

 cytes 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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