242 BEATRICE WHITESIDE 
epithelium. However, this organ no longer represents an undi- 
vided sac, but now ee in some parts of two parallel tubuli 
(fig. 5). This is brought about by division of the formerly 
single sac. The division does not take place in any fixed region, 
but may apparently occur in any part. ‘There is great variability 
in this respect in the different larvae which I examined. The 
only thing which could be ascertained definitely in regard to the 
region in which the division of the saccus occurs, is the fact that 
the division never takes place within the region of the foramen 
endolymphaticum. In the specimen described here as stage 
III, the left saecus endolymphaticus is divided a little behind the 
foramen endolymphaticum into two parallel tubuli running from 
the front to the back (fig. 5). The median one has the greater 
diameter. These tubuli run a short distance toward the back and 
then join again. There is a similar division in the anterior part 
of the right saccus endolymphaticus, in the region of the lobi 
optici. Not only is the region in which the saccus divides not 
always the same, but the manner of division also varies. Some- 
times the tubuli are formed by invagination and adhesion of the 
dorsal and ventral walls of the saccus, in other cases the invagina- 
tion proceeds from the ventral wall only and continues until 
it reaches the dorsal side (fig. 5, d.t.). All parts of the saccus 
endolymphaticus are filled with calcareous matter. 
Stage IV (figs. 6, 13,and 17) 
A larva of 12 mm. length corresponds to stage IV. No trace 
of limbs is apparent. 
The saccus endolymphaticus extends fore the hemispheres — 
into the region of the seventh vertebra (fig. 13). This stage 
is particularly interesting because several subdivisions of the 
saeccus can now be distinguished. Starting from the foramen 
endolymphaticum, the pars anterior of the main stem ‘runs, as 
in the preceding stage, dorsal to the brain as far as the lobi 
optici. Here it fastens itself to the lateral circumference of the 
middle brain, expands a little in the niche between the labyrinth 
and the eye and reaches the posterior part of the hemispheres. 
At its cranial end it sends out a process which ascends obliquely 
