Because of the variable specific longevities, it is frequently difficult to decide when an animal is senile. Man is said to be as old as his arteries, and his span of life nowadays is in the neighborhood of half a century. Parrots exhibit lesions of the vascular system comparable to the arteriocapillary fibrosis of human beings, and their expected longevity is about the same or a little greater. From a study of our cases of this lesion in parrots it can be said to appear quite early in life and not to lead to organic disease as it is alleged to do in man. It is, however, interesting to note that in those animals which are supposed to have the longest specific lives—elephants, snakes, anserine and raptatory birds, parrots—there is relatively low mortality and fewer infectious diseases are encountered. The last part of this statement should be qualified by stating that anserine birds and parrots are quite susceptible to mycoses, in all probability from musty food, which raises their death rate, but as this is accidental and artificial, it can be excluded from consideration. In a rough way there is a direct relationship between the size of an animal and its longevity, but this is not close enough to be a reliable guide; whales and elephants live a long time, but so do snakes and parrots. Within orders this relation of size and expected longevity is more easily seen but is not absolute. I cannot state, according to my present studies, that there is an unqualified relationship between the size and expected longevity of an animal and its pathological lesions. The immediate surroundings and the management of captive animals have a very direct and important bearing upon the mortality and perhaps upon the incidence of morbid processes but probably not upon the character of the latter. A full knowledge on the part of the personnel of a zoological society concerning the habits and habitat of every animal in their keeping is essential, to which must be added a group of interested keepers. In engaging the last, it should not be forgotten that certain men have “a way” with animals and that others cannot manage themselves.