Thus Dr. Oscar Riddle, while admitting that the thymus gland in man has some influence on the growth of the bones, contends that the newly-discovered function of this gland in birds is much more important, since without it none of the vertebrates, excepting mammals, could reproduce their young. “It thus becomes clear,” he says, “that though the thymus is almost without use in the human being, it is in fact a sort of ‘mother of the race.’ The higher animals could not have come into existence without it. For even while our ancestors lived in the water, it was the thymus of these ancestors which made possible the production of the egg-envelopes within which the young were cradled and protected until they were ready for an independent life.” (_Science_, Dec. 28, 1923, Suppl. XIII, XIV.) This conclusion, however, is far too hasty. For, even if we disregard as negligible the minor function, that Riddle assigns to the thymus in man, there remains another possibility, which H. H. Wilder takes into account, namely, that the thymus may, in certain cases, be a temporary substitute for the lymphatic vessels. Having called attention to certain determinate channels found in some of the lower vertebrates, he tells us that these “can well be utilized as adjuncts of the lymphatic system until their function can be supplied by definite lymphatic vessels.” He then resumes his discussion of the lymph nodules in mammals as follows: “Aside from the solitary and aggregated nodules, both of which appear to be centers of origin of lymphocytes, there are numerous other places in which the cellular constituents of the blood are developed. Many of these, as in the case of the aggregated nodules of the intestines, are developed within the wall of the alimentary canal and are therefore endodermic in origin. These include the tonsils, the _thymus_, and thyroid glands, the associated epithelial bodies, and, perhaps, the spleen.... In their function as formative nidi for the cellular elements of the blood these organs form physiologically important auxiliaries to the vascular system as a whole, but belong elsewhere in their anatomical developmental affinities.” (“History of the Human Body,” 2nd ed., 1923, p. 395—italics mine.)