Hypophyses of mice ranging from birth to 150 days of age of both sexes were examined in this experiment.
1. Acidophile cells which were found in only small numbers at immediately after birth showed a gradual increase in number and size with advancing age, and at about 30 days of age many acidophiles showed, though small in size, a similar appearance as seen in adults. At about 60 days of age the cells attained a fully developed state in cytological detail. The number of acidophiles indicated a slight de- crease at the age of150 days. On the other hand, as far as the aci- dophiles were concerned, there was found no significant difference be- tween both sexes throughout this experiment.
2. Two types of basophile cells could be distinguished. The delta-cell, which contains PAS positive, fine cytoplasmic granules, was situated mainly in the anterior portion of the anterior lobe and partly in the central area of the lobe, and the beta-cell which reacts positively with aldehyde-fuchsin as well as with PAS reagent was located in the central region of the lobe. The presence of the former was faintly recognized at a time immediately after birth, while the latter was almost not found till about 10 days of age. These two types became clearly distinguishable at about 20 to 30 days after birth.
3. At 40 to 50 days of age, marked sexual differences occurred in the delta-cell. In females at this stage delta-cells with hyaline vacuoles in the cytoplasm were encountered frequently, and their cytoplasmic granules decreased in number and size when compared with those at just before this stage. On the contrary, in males, such a phenomenon concerning delta-cells did not occur. Thus, in adults, delta-cells in males predominated those in females in number and size, although in males the cells with cytoplasmic hyaline vacuoles were far less in number than in females.
4. As far as the beta-cell was concerned, there was found no difference between both sexes throughout this experiment.
5. In females, a marked occurrence of the“ peculiar chromophobe cell” was observed from the 40th day on, although these cells were only rarely encountered in males throughout this experiment. The cells possessed an eccentrically situated, somewhat dark or vesicular nucleus and a cap-like structure consisting of many basophilic filaments at the cell periphery.
6. The increase in number of the acidophile cell depended mainly on mitotic division of the cell itself and partly on a transition from chromophobe cells. On the other hand, the number of basophile cells increased almost entirely by means of a transition from chromophobes.
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