240 BEATRICE WHITESIDE 
the whole region of the saccus endolymphaticus into two lamellae, 
which unite ventral to that structure. The saccus endolym- 
phaticus is closely connected with the periosteal lamella of the 
dura, whereas it is joined loosely, if at all, to the neural lamella. 
Above the plexus of the fourth ventricle a union of the saccus 
endolymphaticus and the neural lamella of the dura takes place 
with the primary vascular membrane. O’Neil’ proved that 
the division of the dura into two membranes is much less marked 
in the salamander in consequence of the much smaller expansion 
of the saccus endolymphaticus. 
As ean be seen in figure 3, there is at this stage a difference 
between the histological structures of the ductus and saccus 
endolymphaticus. Both organs are lined with a one-layered 
epithelium, but the walls of the ductus are thicker than those of 
the saccus. They consist of cylindrical cells whose nuclei lie 
in the center. The walls of the saccus are composed of low plate- 
epithelium cells, which, in transverse sections, show polygonal 
dividing lines. These cells have their large oval nuclei in the 
center. Many dark pigment granules are found in the proto- 
plasmic part of the cells. The saccus is surrounded by a connec- 
tive-tissue membrane. 
In this stage the saccus endolymphaticus still appears as an 
undivided sac, and has not yet the character of a gland. In 
spite of this fact, I found many lime erystals within the sac. 
This indicates that the cells are able to produce lime from the time 
of their formation—a fact which will not surprise us, if we re- 
member that these cells originally came from the labyrinth. 
Stage III (figs. 4, 5, and 12) 
Stage III corresponds to a larva of 11 mm. length, which does 
not show any visible indication of extremities. 
Figure 12 shows the extension of the saccus endolymphaticus. 
Compared to stage II, there is only a simple increase in length 
in a craniocaudal direction to be noticed. ‘The saccus now ex- 
tends from the optic lobes to the end of the medulla oblongata. 
The course of the anterior part is as follows: Starting from the 
