On the other hand, the cæcal appendage in man is frequently obliterated, there being no trace of the normal aperture, so that there is no connection between it and the general digestive cavity. According to Ribbert,[74] nearly one person in four possesses the appendage in an obliterated condition, the condition being particularly frequent in the aged. In young persons and infants the aperture of the appendage is usually open. In cases where there is no communication with the cavity of the digestive tract, the processes of digestion appear to be normal. It is logical to conclude that in the human being the function of the cæcum is either absent or very slight. Even in the anthropoid apes the appendage of the cæcum appears to be a rudimentary structure, with a function at most accessory to that of the lymphoid clumps. In lower old world monkeys the vermiform appendage does not usually exist, cases such as that of _Cercopithecus sabaeus_, in which it is present as a little boss, being rare. It is necessary to seek the purpose of this structure still lower in the scale of life. In some herbivorous creatures the cæcum is large, and ends in a portion richly provided with lymphoid tissue, and similar to the vermiform appendage. The rabbit and certain marsupials are good examples. Undoubtedly, in their cases, the portion of the digestive canal which corresponds to the vermiform appendage of man is active in the digestion of vegetable matter. The organ is a very old part of the constitution of mammals, and it is because it has been preserved long after its function has disappeared that we find it occurring in the body of man. Rudimentary organs for the most part display a congenital lack of the power of resistance, and, as Darwin suggested, for this reason they are frequently the seats of disease. When Darwin wrote his work on the “Descent of Man,” more than a quarter of a century ago, many fatal cases of inflammation of the appendage had not been recorded. Darwin quoted only two cases as known to him. Since then, appendicitis (the name given by American surgeons to the first acute or to the chronic inflammation of the appendage) has become a well-known disease in Europe and America, and occupies considerable space in treatises on the pathology of the digestive tract.