DEVELOPMENT OF THE SACCUS ENDOLYMPHATICUS ZO 
These last-mentioned structures attain their definitive form at 
the end of the metamorphosis. 
At the time of its first appearance, the saccus endolymphati- 
cus is an undivided sac lined by a single layer of epithelium. It 
soon becomes partitioned into two tubuli which later subdivide 
into smaller ones. During the course of development, the saccus 
is divided more and more into small tubuli until it finally has 
the appearance of a glandular structure. 
The histological structure of the cells lining the saccus endolym- 
phaticus remains practically the same during the whole period 
of development. ‘The cells are first cylindrical in shape, later 
they are cuboidal. Blood vessels are present at first only in 
small numbers, but later become very numerous. The calcareous 
contents of the saccus exist almost from the very beginning. 
Throughout the entire course of development, no part of 
the saccus endolymphaticus suffers retrogression, its develop- 
ment is a continuous and direct one. Its development also 
proceeds very slowly. For these reasons, it is certain that 
the saccus endolymphaticus of the frog does not represent a 
larval organ. 
REMARKS ON THE STRUCTURE OF THE DUCTUS AND SACCUS 
ENDOLYMPHATICUS IN THE VERTEBRATA 
Since the investigations of Hasse (’73) and Retzius (’81), 
no comparative-anatomical study of the ductus and saccus 
endolymphaticus has been made, although some very interesting 
papers on this organ in individual Vertebrata have been pub- 
lished. Unfortunately, not all vertebrate types have been 
examined in regard to this particular structure. It is, however, 
possible to draw some conclusions from the facts hitherto ascer- 
tained. Therefore, I shall give a short description of the anatomi- 
cal structure of these organs, based on the above-mentioned 
works and the more recent reports. 
Hasse writes: 
Saemtliche Wirbeltiere besitzen eine aus dem Vestibulum sich erhe- 
bende Roehre, die, mit Ausnahme der Plagiostoma, wo dieselbe auf 
die Schaedeloberflaeche fuehrt, bei allen Tieren in die Schaedelhoehle 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 30, NO. 2 
