The changes in atrophy consist in irregular distortion of the gland by fibrous tissue to which may be added large colloid or fluid cysts. There is no uniform finding in the thyroid for the diseases believed to be due to its atrophy, functionally at least, namely cretinism and myxedema. In the former there may be no thyroid, or it may rather closely resemble the normal organ while in the latter definite scarring and distortion is the rule. The gland acini are compressed, the cells vacuolated or crushed out of existence or there may be colloid cysts. Inflammations occur as swellings of the interstitial tissues and of the acinus cells during many acute infections. Repetitions of this may leave a definite increase of connective tissue with large cells in the acini, a lesion which many observers have looked upon as underlying certain goitres and myxedema. HYPERPLASIAS. The cause of progressive hyperplasias has been ascribed to infection, to chemical substances in water and food, endogenous toxins, heredity and many other factors. While we can add nothing definite in this matter it is worthy of notice that all our animals are exposed to the same general climatic conditions, receive the same water, are fed from the same stocks and many varieties may be in charge of the same keeper. The influence of preëxisting infections cannot of course be measured. Inbreeding or captive breeding seems to have a very definite effect upon thyroid insufficiency as is well known and so sharply emphasized by McCarrison in his reference to intermarriage among certain Moslems; I shall cite the history of a wolf bitch which gave birth to three cretin litters while apparently well but mated to a goitrous male. These facts concerning the etiology are given merely to emphasize the high degree of probability that the distribution of the lesions of the thyroid gland among our specimens indicates the susceptibility of the various orders. This perhaps needs no emphasis for the carnivores, but it does for the marsupials. The literature contains many references to goitre in domesticated ungulates; this would give the impression that they are common among them, and so they may be, but this is not the case for wild ungulates. There being no doubt that the Carnivora have the highest incidence of thyroid enlargement, man being especially prone to it, and since goitre may be induced in fish by feeding meat, the inference is direct that high protein diet stands in some relation to this condition. Thirty-nine of our sixty thyroid lesions occurred in the order Carnivora; all the families of land varieties are represented; 8.1 per cent. of the specimens coming to autopsy showed definite thyroid alterations. However, marsupials have also a decided thyroid vulnerability as indicated by 4 per cent. of the specimens presenting abnormalities at death. Four of the seven cases were among the carnivorous opossums and “devils,” the remaining three being in herbivorous kangaroos.