The amount of thyroid tissue possessed by an animal might be judged by measurement or weight. The former is misleading since the density might vary, as it certainly does in the two classes and between certain orders in mammals. Actual weights would afford little comparison, whereas the weight in terms of total body weight may supply a guide to the amount of gland normal to an animal. There are given in Table 15 the grams-per- kilogram-body-weights of the thyroid bodies (thyroid and parathyroids both sides combined) of twenty animals whose gland seemed entirely normal at autopsy. They are all adult specimens, free of cretinoid characters and of bone or heart diseases, conditions which might reflect abnormalities to these glands. The list is too small to warrant any conclusions, but in one respect confirms Murray’s[41] observation and certain experimental work, notably of Vincent and Jolly[42] and Carlson, Rooks and McKie[43]. The carnivores have more thyroid than ungulates (averages .55 gm. _vs._ .18 gm.), but the marsupials on our list have nearly as high an average as the former, namely .44 gm. To these figures might be added others which I have worked out from the list given by Murray; it is only possible to compute the gram-perkilogram value for a few of his examples since the body weights are not given in all. Using 2.2 pounds as equal to one kilogram, the seal of 432 kilos had .03 gm. of thyroid, lion had .18 gm., leopard had .46 gm., a serval .36 gm., a skunk 2.35 gm., (was this normal?) while a single herbivore with the weight given was a porcupine having .25 gm. per kilo. The average of Murray’s carnivores is therefore .67 gm. per kilo of body weight, whereas our figure is .55 gm. That the incidence of thyroid abnormalities stands in direct relation to carnivorous character has been recognized before, and is abundantly borne out by our statistics, as will appear at a later place.