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The thyroid, which in the adult is a complicated ductless gland, has in the young Ammocoetes the form of a longitudinal groove of the ventral wall of the pharynx.

Thymus, thī′mus, n. a ductless gland near the root of the neck, of no known function, vestigial in adult man—that of veal and lamb called neck-sweetbread.

At the present time the tendency among some writers is to make the ductless glands the responsible agents in almost all diseases.

The spleen and the bone marrow were being used in the anemias, the ductless glands in various nutritional diseases and even extract of heart for heart disease.

In most of the extreme cases the dwarfing is the result of some defect in the ductless glands which regulate the normal growth of the body.