Japanese medaka (Oryzias latipes) and channel catfish (Ictalurus punctatus) were investigated for carcinogenic response following a 28-day, 3X/wk pulse exposure to N -methyl-N '-nitro-N -nitrosoguanidine (MNNG). Five-wk-old medaka were exposed at concentrations of 0, 0.5, and 1.0 mg/L, and 5-mo-old catfish at concentrations of 0, 0.1, and 0.5 mg/L. In medaka, a total of 19 tumors including 2 branchioblastomas, 6 thyroid follicular adenomas and 1 adenocarcinoma, and 11 subcutaneous fibrosarcomas were observed in 16 of 96 MNNGexposed fish. In catfish, a total of 37 tumors including 4 squamous cell carcinomas and 16 papillomas, 3 lipomas, 1 fibroma, 1 osteosarcoma, 4 branchioblastomas, 6 thymic epithelial tumors, and 2 generalized lymphosarcomas were observed in 34 of 172 MNNG-exposed fish. The induction of neoplasms in medaka was primarily in the gill, thyroid, and subcutis of the cervical and trunk regions, whereas in catfish skin, thymus, oro-pharynx, and hemopoietic tissues were also commonly affected. In both species, the neoplastic response was considered to be related to direct exposure of the tissues to MNNG. Some of these tumors have not been reported in the literature in either natural or experimental fish. The results also suggest species-specific differences in carcinogenic response following MNNG exposure.

189Summary A case of opocephaly in inbred guinea-pig strain 2jN and another in strain 13jN, a conjoined twin and an opocephaly concurrent with conjoined twins in the Dunkin-HartleyjFD strain are described. The incidence of congenital malformations in the inbred strain 2jN and strain 13jN was 0,0013 and 0,0073 % respectively. The incidence in the random-bred Dunkin-HartleyjFD strain was 0'0007%.Spontaneous congenital malformation of the guineapig have rarely been reported (Hoar, 1976). This is especially remarkable in view of the enormous numbers of guinea-pigs that are constantly being raised as laboratory animals. In a recent review of Case I. A conjoined twin Dunkin-HartleyjFD strain guinea-pig was found dead shortly after birth. The female twins had a single head with a broad face and 2 eyes. The upper abdomen was shared; the lower abdomen and hind quarters were separate and normally developed (Fig. ]). The fused thoracic cavities had 2 sterna, but only] normal respiratory system of larynx, trachea and lungs. There was a

The foetuses were completely developed and were found in the peritoneal cavities of strain 13/N guinea-pigs in their 3rd pregnancies. One foetal placenta was attached to the left side of the peritoneal wall, the other adhered to the pyloric region of the stomach.