Embryology and Maturation 3 1 



present at birth and full development of the gland awaits maturity 

 of the animal (3-6 months) (Leeson and Jacoby, 1959a; Screebny, 

 Meyer, Bachem and Weinman, 1955; Leeson, 1959). 



This extreme case illustrates the general conclusion that acinar 

 cells are a late development of the gland, and at least in the rat and 

 probably other rodents very active saliva secretion can occur in the 

 absence of acini. Little use has been made of a developmental 

 approach to attempt to dissect the secretory function of the salivarv 

 gland, but it might well be a fruitful one. Leeson and Jacoby 

 (1959a and b) and Leeson (1959) describe the development of the 

 rat submaxillary gland in great detail and find that at birth the 

 large interlobular ducts already show basal striation (and infold- 

 ings), the intralobular ducts are small and merge into a rudimen- 

 tary intercalated duct or terminal tubule. These terminal tubules 

 are formed of columnar cells with basal nuclei, extensive cyto- 

 plasmic granulation and a well-developed endoplasmic reticulum. 

 Two weeks after birth crescent-shaped buds of the terminal 

 tubules form the primordia of the acini which begin to appear 

 shortly afterwards. At six weeks acini are well developed, as are 

 the intercalated ducts. The early development of the duct system 

 is accompanied by ingrowth of blood vessels (Flint, 1902-3) and 

 this pattern persists in the mature gland (see p. 15), the vascular 

 tree of the acini appearing to have grown out of that of the ducts. 



In rodents the subsequent development of the gland is compli- 

 cated by hormonal effects. In prepubertal mice the tubules consist 

 of cubical cells with central nuclei and clear cytoplasm. In adult 

 females the cells are more columnar, some are vacuolated and 

 others show dark granules in the apical cytoplasm. On the other 

 hand, in adult males the tubules are comprised of large cells with 

 basal nuclei and mitochondria and the cytoplasm is packed with 

 granules (Lacassagne, 1940; Junqueira, Fajer, Rabinovitch and 

 Frankenthal, 1949). This interesting dimorphism has been the 

 subject of numerous investigations, which have shown an atrophy 

 of the tubules in castrated males (Shafer and Muhler, 1953; 

 Junqueira, 1949) corrected by testosterone, and a depression of the 

 size of the female tubules by stilboestrol. These tubules are also 

 affected by thyroid hormones (Grad and Leblond, 1949; Bixler, 

 Webster and Muhler, 1957; Raynaud, 1950) and atrophy after 

 hypophysectomy (Screebny, Meyer and Bachem, 1953; Lacas- 

 sagne and Chamorro, 1940). The atrophy after hypophysectomy is 



