Joseph Marshall Flint i 
gradually becoming firmer and more definite and the exoplasmic fibrils 
that run out into the adjacent syncytium are 
confined into smaller sharper bundles. These, 
with the progressing age of the embryo, have 
more definite and distinct characteristics. 
The fibrils are of unequal size and often run 
so that a definite cross hatch is seen along 
course of the fascicuh. In the syncytium 
there is very little granular debris, the dotted 
or granular appearance noted along fibril 
bundles or at their nodes being due to the . 
intersecting strands of exoplasm cut in cross- 
section. 
In a pig 22 em. in length the alveoli are 
very closely approximated and the strands of 
Fig. 6. 
the submaxillary gland of 
pig’s embryo 19 cm. long. 
Many of the basement mem- 
branes are now in apposition, 
although their identity is still 
distinct. Stained by Mallory’s 
method, after Zenker’s fluid. 
exoplasm bridging the spaces between them 
are very sharp and take a deep clear blue 
stain. In places, the membranes which are 
now sharp and distinct are in close apposition 
2B TEE GO 0S with those of adjacent alveoli, although in 
some parts of the lobule, particularly the central region, there is still 
a considerable amount of general syncytium. Between the alveoli are 
bridges of exoplasm, in the mesh-work of which the connective tissue 
cells now lie. This portion of the syn- 
cytium becomes the interalveolar frame- 
work. These have differentiated and show 
several types, some and some 
branched. At points where the alveoli are 
in apposition the nuclei are flattened out 
between them so that they now form in 
these situations elongated lanceolate-shaped 
nuclei which stain with the orange element 
of the dye and show an extremely granular 
structure. Those out in the looser syn- 
eytium still retain their spherical or ovoid 
contour and still show a poorly-marked nu- 
cleolus. 
In the submaxillary of a pig two days old 
the alveoli are now almost entirely in appo- 
sition with each other. Here and there, 
one may find slight chinks or clefts where the basement membranes of 
round 
Fig. 7. 
of pig’s embryo 22 cm. long. 
Stained by Mallory’s method. 
Submaxillary gland 
Zenker’s fluid. 
diameters. 
Magnified 900 
