INTEGUMENT OF NECTURUS MACULOSUS 561 
were found within the gland lumina, and it was evident that the 
remains of the secreting cells were being removed (fig. 22). 
Meanwhile, in these discharged glands considerable activity is 
noted at the intercalary region and, as the old epithelium is 
removed, there is developed from this position a new secretory 
epithelium. In figure 22 an early stage in this replacement of 
the old epithelium by a new one is shown. From all around 
the interealary region cells move down along the old gland wall, 
forming a continuous layer. Apparently the intercalary region 
is unable to furnish enough cells for the complete repair of the 
gland, and after this supply has been exhausted, cells migrate 
downward directly from the epidermis not only from the germina- 
tive layer, but also from the transitional layers around the duct. 
Evidence for this conclusion is supplied from conditions like 
that shown in figure 23. In this gland the intercalary region 
has disappeared and in the duct the epidermal cells present an 
amoeboid appearance. Further, in other glands in which a new 
epithelium has been completely developed, the duct is very 
large, indicating that some of the cells now found in the body. - 
of the gland may have migrated down from its sides. Mitosis 
may also play some part in increasing the number of cells (fig. 29). 
The epithelial cells derived from the intercalary region and 
epidermis gradually move downward and are arranged eventually 
to form a single layer over the entire muscular wall which is 
seemingly preserved intact. The new cells are soon definitely 
orientated radially to the center of the gland lumen, and assume 
the form and appearance already described for potential granular 
cells. They are closely packed, tall, and columnar. Their 
cytoplasm is clear and marked with fine lines, and on the ends 
of the cells clear, club-like masses project into the lumen (fig. 
23). Later stages (fig. 29) show the gland cells becoming reticular 
and beginning to elaborate secretion. In fact, the replacing 
epithelium appears to follow exactly the developmental stages 
already outlined for the gland bud which arose as an invagination 
from the germinative layer of the epidermis. 
In the discussion of mixed glands reference was made to ae 
was apparently a permanent mixed condition (fig. 36). It will 
