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Pathological changes attributable to cadmium poisoning were observed in the intestinal tract, the kidney, and the gills of Fundulus heteroclitus after exposure to 50 ppm of the metal. Microscopic examination revealed pathological changes of the intestinal tract as early as 1 hr after exposure, in the kidney after 12 hr, and in the gill filaments and respiratory lamellae after 20 hr. These manifestations of cadmium poisoning bear resemblance to the pathological changes that have been demonstrated clinically and experimentally in mammals.The examination of circulating blood elements revealed rapid and striking changes among cells of the eosinophil lineage. The abundance of eosinophils increased steadily to a level approximately 45% above the usual amount. Indications of the cellular increase occurred as an early rise 4 hr after exposure.A reduction in the relative numbers of mature eosinophils was evident in imprints of head kidney tissue. Nuclear anomalies were associated with the thrombocytes of specimens after 8 hr exposure; however, these changes were not noticeable at either earlier or later time periods.

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Comparative histology of gonadal neoplasms in 14 marine bivalve species or hybrids from 5 countries described in the literature and/or archived in the Registry of Tumors in Lower Animals (RTLA), Washington. DC. USA, revealed 3 basic histotypes. Hundreds of cases were of germ cell origin with hfferent stages of development. They consisted of undifferentiated germ cells that filled individual follicles (stage l ) , were present throughout the gonadal area (stage 2), or had spread to outlying tissues (stage 3). Five cases were of stromal origin. The connective tissue comprising these tumors ranged from vesicular to myxoid to spindle-cell. As these tumors grew, they invaded and destroyed normal follicles. Three cases representing a third histotype appeared to be of both germ cell and stromal origin. Two of these 3 were among 15 Crassostrea virginica recently collected from the Pawcatuck River, Rhode Island, USA. In the most advanced case, basophilic hypertrophied neoplastic germ cells were rapidly proliferating along the walls of gonadal follicles and the ducts that extended into the mantle, while the central region of the tumor mass was densely flbrous. Some neoplastic cells in follicles adjacent to normal ova-bearing follicles were differentiating into spermatocytes. Tumor cells aggressively crossed the follicular basement membrane, invaded the vesicular connective tissue supporting the gill axis, and formed a cystic mass along the lumina1 wall of the branchial vein. The less advanced C. virginica case had a smaller, less aggressive tumor but its basic features were similar. The third case similar in composition, pattern, and behavior was in a C. gigas that had been collected during the 1960s from the Willapa Bay. Washington, USA, and had originally been interpreted as a fibroma. All 3 of these mixed gonadal-stromal neoplasms are presently diagnosed as gonadoblastomas.