140 THE AMERICAN MONTHLY [May, 



duced is a camera-lucida drawing from an ordinary sec- 

 tion of the organ. The bulk of the organ is composed of 

 the alveoli or final parts of the system of ducts, one of 

 the ducts with its branches is seen, cut for a part of its 

 length, it is not .seen to open into the alveoli, because a 

 view of this is rarely attainable in sections, though it is 

 sometimes to be seen. Running beside one of the branches 

 of the duct is seen the artery. The spaces between 

 these parts are occupied by the connective tissue or by 

 the capillaries or nerves, which are hardly distinguish- 

 able from the areolar connective tissue. The cells of the 

 alveolus are of two sorts. There are first the "serous 

 cells" which compose the bulk of the organ. Tlie&e cells 

 are shaped like spherical wedges and hence appear tri- 

 angular in sections. The cells do not wholly fill the al- 

 veolus, each one is a trifle shorter than half the diameter 

 of the alveolus thus leaving a small space in the centre, 

 called the "lumen." The lumen is in communication with 

 the hollow passage in the centre of the duct. The serous 

 cells are of a particular shape and character, they are 

 comparatively clear, and their nucleus is small and flat- 

 tened in the plane of the base of the cell, it also lies near 

 to the base, so that in some cells it is hardly noticeable 

 at all. There is another kind of cell in salivary glands 

 called the "mucous" cell, this is not found in the parotid 

 gland of the cat, it is characterized structurally by the 

 fact that the nucleus is spherical and occupies the centre 

 of the cell. The bases of some of the cells of the alveo- 

 lus are clasped or covered by dark deeply stained cells, 

 called " demi-lune " cells, there are a few only of these to 

 each alveolus, and hence they are not seen in all the parts 

 of the section. The duct is also lined with cells which 

 become evident in sections after study, the side walls of 

 the cells are rarely seen, but the nuclei are regular in po- 

 sition and from their shape and position one must infer the 

 position of the side wall. These cells are tall and expose 



