Joseph Marshall Flint 435 
this author does not describe the vascular units in the different circula- 
tory systems as such, nor does he consider the capsular and septal circu- 
lation and their relations to that within the lobules. 
The alveolar capillaries are not situated in the lymph spaces, as 
Kowalewsky believes, but in the interalveolar spaces between the base- 
ment membranes of adjacent acini. Here they are limited by the retic- 
ulum fibrils that bind together the alveoli which they supply. 
DEVELOPMENT OF THE ALVEOLAR EPITHELIUM AND THE DEMI- 
LUNES OF GIANUZZI. 
‘In a pig 3 centimeters long (Fig. 9) the terminal buds of the branching 
column of cells forming the ductus submaxillaris indicate the primitive 
alveolus in its 
simplest form. It 
is composed of a 
group of irregu- 
lar polygonal 
cells embraced 
and enclosed in a 
reticulated base- 
ment membrane. 
1.9. Sectionof primitive Outside of a 
eiyacin fconia cab eel . . Fig. 10. Alveolus from glandula 
of pig’s embryo 3centimeters slightly definite submaxillaris of pig’s embryo 8 
long. Hardened in Zenker’s 
fluid, stained by Mallory’s 
method. x 650 diameters. 
This drawing shows the ir- 
regular columns of the cells 
forming terminal bud orapex 
of the growing column of 
cells in the developing sub- 
maxillary. 
arrangement of 
the outer layer 
of cells, the re- 
mainder are 
centimeters long. Hardened in 
Zenker’s and stained by Mallory’s 
method. 650 diameters. The ar- 
rangement of the cells in two or 
three layers about the lumen isnow 
apparent, together with the begin- 
ning of the formation of the mucous 
globules within the cells of the 
inner layer. 
packed —_irregu- 
larly within the alveolus. The cells are polygonal in shape, have a 
definite outline and granular cytoplasm, staining a golden brown by 
Mallory’s method. ‘The nuclei are vesicular or ovoid, have a distinct 
nucleolus and considerable chromatin deposited on the linen threads. 
Exclusive of the regularity of the arrangement, there is, however, no 
morphological difference at this stage between the cells of the central 
and peripheral portions of the acinus. In a pig 8 centimeters long 
(Fig. 10) a lumen has appeared in the center of the developing alveolus 
and the cells are arranging themselves in two or three fairly definite 
layers. No marked changes are observed in the character of the parietal 
group of cells, but in those of the inner layer of the lumen of the 
