444 The Submaxillary Gland 
assumed with safety that “ the angiology of an organ is in a measure the 
recapitulation of its ontogeny.” 
5. The epithelium of the ducts in early embryos consists of a solid 
column of cells. At an early period the lumen is formed and the cells 
arrange themselves in two fairly definite layers. As the ramification 
of the cell columns proceed, the penetration of the lumen extends upward 
until all the ducts as far as the small terminal buds have a double layer 
of cells. In a pig 8 centimeters long the lumen appears within the 
alveoli, the first formation of the ampullae. The size and definition of 
the duct epithelium increase up to the time of the adult, the cells increas- 
ing chiefly in size. At the period just before birth mucous goblet cells 
appear in among the columnar epithelium and the inner layer of the 
larger ducts. The fibrillation in the external portion of the cells lining 
the intralobular ducts is not manifest in sections stained by Mallory’s 
method until after birth. Usually the ducts of the intralobular system 
appear to have but a single layer ef cells in the adult, although in some 
cases, particularly in the intercalary duets, one finds an occasional double 
row. 
6. The alveolar epithelium consists in the pig 4 centimeters long of 
a solid group of polygonal cells. At a little later period these cells ar- 
range themselves in two or three indefinite layers about the lumen or 
ampulla of the alveolus. In the cells of the inner layer mucous globules 
begin to appear. ‘These increase in size until they finally reach the 
basement membrane, leaving the cells of the outer layer in the interstices 
between the bases of the mucous cells. In this way the mucous elements 
of the alveoli are formed from the cells of the inner layer, while the 
demilunes of Gianuzzi are derived from the parietal cells. In following 
so definitely the ancestry of the demilunes, it become obvious that they 
are definite elements in the alveolus and are neither mucous cells in one 
or another stage of activity, nor do they represent young mucous cells. 
In conclusion I wish to express by thanks to Dr. A. W. Lee, of this 
department, for the painstaking care he has taken in the production of 
these drawings. 
