Much attention is focused on environmental contamination by heavy metals. The heavy metal mercury is found worldwide and is ranked number 3 on the Comprehensive Environmental Response, Compensation and Liability Act substance list. We examined the effect of low-level methylmercury exposure on central nervous system development of wild-type zebrafish embryos (ZFEs) of the AB strain because methylmercury is the most common form of mercury to which humans are exposed in the environment. ZFEs were exposed to nine different concentrations of methylmercury [0 (negative control), 5, 10, 50, 80, 100, 200, 500 and 1000 parts per billion (μg l(-1) )] starting at 6 h post-fertilization, which is the time the neural tube is first beginning to form. ZFEs were exposed to 2% ethanol as positive controls (100% embryonic death). ZFEs were assessed at 30, 54, 72 and 96 h post-fertilization for changes in embryonic development, mortality, time of hatching and morphological deformities. No abnormalities were observed in ZFEs exposed to 5 μg l(-1) methylmercury. The time of hatching from the chorion was delayed in ZFEs exposed to methylmercury concentrations of 50 μg l(-1) or higher. Significantly more ZFEs exposed to 0, 5 or 10 μg l(-1) methylmercury successfully completed hatching compared with ZFEs exposed to 50 μg l(-1) or higher methylmercury. ZFEs exposed to more than 200 μg l(-1) methylmercury exhibited 100% embryonic mortality. The rate of cell proliferation within the neural tube was significantly decreased in embryos exposed to 10, 50 and 80 μg l(-1) methylmercury and there were no differences between these doses.

Tongue specimens were collected from 18 healthy adult Egyptian geese (Alopochen aegyptiacus) of both sexes. We measured and analyzed the whole, anterior, middle and posterior length and width of the tongue parts. The dorsal mucosal surface of each tongue was investigated by SEM. The length of whole tongue, widths at anterior and middle ends of its root showed significant differences between sexes. By gross morphology, the tongue showed 3 parts (anterior, middle and posterior). The anterior part represented 1 half of the tongue, while the 2 remaining parts comprised the other half. A clear median longitudinal groove was observed macroscopically along the forward half of the anterior region. The caudal part of the body had a central circular depression in front of giant conical papillae arranged in transverse row. On both sides of the tongue, cylindrical lingual papillae were compactly distributed and divided into anterior and posterior groups which increased in size and decreased in number caudally. By SEM, both giant conical and large cylindrical lingual papillae were lined with extensively modified mucosal surfaces that appeared as finger-like projections with scales. The tongue, which plays an important role in food intake in Egyptian geese, exhibited significant morphological variations in dorsal mucosal lining between sexes. Morphological observations recorded significant gender differences in total length and widths of the tongue at anterior and middle segments of its root.

Ten adult domestic Mallard ducks and ten adult domestic pigeons of both sexes were used for morphologic and histological study. The proventriculus was the last part of the foregut. It was cone-shaped in pigeon while it was tubular in duck and arose from the esophagus. The

Teratology of Aflatoxin in Rabbits El-Nahla et al.

Ten adult hooded crow and another ten adult cattle egret were used to study the oropharyngeal cavity macro and microscopically. The oropharynx in both birds was a dorsoventrally flattened tube, presented four openings, choanal and infundibular slits in the roof and glottis and oesophageal opening in the floor. The choanal slit divided into rostral and caudal part in hooded crow while in cattle egret it was undivided. The roof of oropharynx presents infundibular slit in midline. The horny conical papillae were widely distributed in the roof and floor of the oropharynx of hooded crow while in cattle egret it was absent except two rows in the roof of oropharynx. The opening of salivary glands ducts were widely distributed in the roof and floor of the oropharynx of the hooded crow while in cattle egret they were few in number only in the caudal part of the roof of the oropharynx. The microfolds in both birds are present in the roof of the oropharynx but absent in the floor. The cattle egret is characterized by the presence of hills and deep microgrooves in addition to micropits.