1. Histological investigations on the development of the abomasal glands of the sheep showed that peptic cells, which contained pepsinogen granules, were present at 85 days and gradually increased in number up to term (150 days).2. Parietal cells, which were very sparse until term, increased rapidly during the first 48 hours of life.3. The abomasal contents during fœtal life were neutral in reaction, and in late fœtal life contained small quantities of a proteolytic enzyme active at pH 2·1. This material also clotted milk readily.4. The reaction of the abomasal contents, which at birth was between pH 6·0 and 7·0, changed gradually during the first two days of life, and 36 hours after birth was adequate for the activation of pepsin, pH 3·0 to 4·0.5. Comparative observations showed that in the young rat the gastric glands were not fully developed until three weeks after birth, whilst the newly born guinea‐pig possessed fully differentiated gastric glands.6. It is concluded that in those species in which antibody transference occurs in utero, secretion of active gastric juice occurs at or before birth, whilst in those species receiving antibodies from the colostrum, gastric protein digestion is delayed by retarded development of the gastric glands or by one of the cell types of the gastric glands.