Seasonal cyclical changes in the thymus of the mallard.

In the course of an investigation into seasonal changes in the endocrine organs of wild mallards (Anasplatyrhinchas p. (L.)), a striking seasonal cycle was found in the thymus affecting both the amount of thymus tissue and its histological structure. This appears to be the first description of changes of this nature affecting the thymus apart from a statement by Jolly (1913) in connexion with age involution of the thymus in fowls, to the effect that this tissue is much influenced by seasonal and nutritive changes. Aime (1912) has described a seasonal regeneration of the thymus in turtles, but it will be shown below that this must be regarded as a different type of response from that found in the mallard.