Observations on dugong histology

SYNOPSIS A description is given, for the first time, of the histological structure of (a) certain lymph nodes, and (b) the thymus and thyroid glands, of the dugong (Dugong dugon). The nodes are of the haanolymph variety and manifest an astonishing range of variation in both the relative proportions and the mutual topographical distribution of their component medullary and cortical tissue. The thymus displays the customary mammalian constitution. The thyroid gland, however, is exceptional in the relatively great abundance and density of its intervesicular stroma; its histological appearance would seem to agree with other evidence favouring the occurrence in the Sirenia of a functional hypothyroidism.