| Summary: | 1. There is no satisfactory evidence for regarding the organ of Syrski as the male gonad of Anguilla . 2. Silvering of the eel, salmon and trout is independent of gonad development and cannot therefore be regarded as a breeding dress. 3. Injection of either pregnancy urine, ox anterior lobe extracts, pig anterior lobe extracts and thyroid extracts, as also pituitary homeo-implantation, were all without effect on the gonads of eels treated in this way. 4. Ox anterior lobe extracts produced premature smoltification in Salmo salar , had no visible effect on S. trutta or on Anguilla vulgaris , and did not affect the gonads in either species. 5. Injection of thyroid extracts produced silvering in salmon and brown trout but had no effect on the eel. 6. After two months' treatment with thyroid extract brown trout are externally indistinguishable from sea trout.
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