抄録
The external and histological features of a remarkable myxoma developed in the righthand side of head skin of an old female salmonoid fish, the Ayu, Plecoglossus altivelis Temminck et Schlegel, that, has tided over the winter, are described. The present example might be recognized as the first record of a myxoma in the fish from Japan.
The tumor is a giant, smooth, hemispherical swelling, including the right nostril, and measuring 13.8 (dorso-ventral axis)×15.0 (cranio-caudal)×7.6 (right and left, i. e., depth) mm. Although the overlying skin, namely, the epidermis, is intact and healthy, the right eye is compressed heavily by the tumorous body. The dermis forms a thick layer, and is chiefly constructed from the well-developed bundles of collagenous fibers and a large quantity of mucoid ground substance. The branches of fibrous strands enter the mucoid substance and partition it into many subdivisions, varying in size and shape. Many lacunae are presented here and there. A large number of stellate shaped cells, probably the fibroblasts, and unde-termined cells in the course of collapse are found in the mucoid substance, which has con-tained abundant fibrills. Just beneath the epidermis the peculiar cells, which seem to be derived from the supporting cells of the olfactory epithelium, show the hyperplastic condition; some of which are arranged in the follicles, surrounding the droplets of mucoid substance in their lumina. The layer of these epithelial components is considerable thick.
Several nodules diagnosed as the lymphosarcoma were recognized in the ovary of this fish; the tumor is probably caused by endocrine derangement. Conseqently, there is no possible relationship between the myxoma of head cutaneous-, and lymphosarcoma of ovarian tissues. Besides, the histological picture of the thyroid gland is appeared to be marked hypofunction.
