Joseph Marshall Flint 5 
much, however, is certain; the formation of the membranes about the 
growing apices of the cell columns which are increasing constantly in 
length and circumference is chiefly by successive deposits of fibrils so 
the layer of syncytium around the growing ducts and alveoli forms what 
may well be termed the deposition zone. In this region the nuclei in 
the earlier stages at least are very numerous. Somewhat further out 
there is a noticeable diminution in their number and in the exoplasm 
and endoplasm are many clear spaces which are apparently filled with 
fluid. The nuclei of the syncytial cells are oval or round, contain a 
very indistinct nucleolus and are in general about the same size as the 
nuclei in the developing cell columns. The membrane itself under 
the highest powers is more or less irregular and, while looking some- 
what homogeneous, still bears in some places definite evidences of fibril- 
lation. There, as in the buccal cavity, the staining of the endoplasm 
destroys to some extent the sharpness of the picture. 
In the submaxillary gland of a pig 4 cm. in length there has been a 
radical change in the syncytium. While it has not entirely differen- 
tiated into endoplasm and exoplasm, the exoplasmic fibrils have become 
extensively anastomotic although somewhat 
short, irregular and ill-defined. Here and 
there they seem matted together by some 
interfibrillar substance which on coagula- 
tion has become slightly tinged with the 
stain and thus destroys to some extent the 
sharp contour of the fibrils. This happens 
often in the best preparations. Numerous 
granules are also found deposited on the 
fibrils or at their nodes. It is also possible 
that these may be displaced particles of 
endoplasm that have become detached from 
the cells and remained entangled in. the 
exoplasmic network. The endoplasm is 
gathered as a small cellular mass about the 
nucleus forming bipolar or multipolar cells. 
In the area just around the apices of the 
growing gland, that is to say, in the deposi- 
tion zone, the arrangement of the cells is 
such that, in general, the long axis of the 
nuclei is parallel with the basement mem- 
brane, while the cells in parts more distant have no such definite 
arrangement. This seems to indicate that the tension caused by the 
Fria. 2. Growing tips of sub- 
maxillary tree with the adja- 
cent deposition zone from pig’s 
embryo4cm. long. Exoplasm 
and endoplasm well differenti- 
ated. Fixed in Zenker’s fluid. 
Stained by Mallory’s method. 
Magnified 900 diameters. 
