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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.

Occasionally diseases of other ductless glands, as the thyroid, may have amenorrhea as one of the first symptoms.

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.