542 A. B. DAWSON 
17 is represented. This consists of a solid mass of cells which 
is already assuming the form of the mature gland. Mlitoses are 
frequent both in the gland bud and in the epidermis above. 
There is as yet nothing in the staining reactions or appearance 
of the cells to indicate whether this is the young stage of a granu- 
lar or of a mucous gland. 
c. Differentiation of the granular gland. Later developmental 
stages show the young gland considerably increased in size with 
a well-defined lumen around which the cells are now definitely 
arranged radially to its center. The increase in size is partially 
due to the formation of the lumen, but there is also an actual 
increase in the number of cells, due both to the division of the 
cells within the gland and to the immigration of cells from the 
epidermis. Maurer (’95), Ancel (’02), Nirenstein (’08), and 
others have described, in the larval development of the glands, 
an early differentiation of the cells of the bud into two layers— 
the outer to form the muscular wall, the inner to form the glandu- 
lar epithelium. This condition is not realized in adult Necturus, 
the cells in early stages of gland formation being arranged in a 
single layer around the lumen and taking on a characteristic 
form and appearance which marks them as being potential 
granular cells (fig. 19). They are tall, columnar, and closely 
packed (figs. 23, 29). Their cytoplasm is very resistant to all 
stains, so that the epithelial layer at this stage always appears 
clear. Within the cells, and running parallel with their long 
axes, fine wavy lines can be distinguished. On the ends of the 
cells, peculiar club-like masses, composed of a clear non-staining 
substance unlike cytoplasm, extend into the lumen of the gland. 
These masses do not appear to be important in the life-history 
of the cell and generally disappear when secreting is begun. 
The nuclei are ellipsoidal and usually lie near the center of the 
cytoplasm, but they are sometimes nearer the bases of the cells. 
Fine filaments have been described in developing poison cells 
by Schneider (’02), Nirenstein (’08), and O. Schultze (11). 
These filaments show an affinity for basic dyes, especially iron 
haematoxylin, and are regarded by Schneider and Schultze as 
taking part in the formation of the secretion granules which, it 
