DEVELOPMENT OF THE SACCUS ENDOLYMPHATICUS 259 
Fleissig (08), Wenig (11), and Keibel (15) think it probable 
that this duct is rightly called the ductus endolymphaticus. 
This structure is not found in the Siluridae, Cobidae, Cyprinidae, 
Percidae, and Clupeidae. 
The anatomical structure of the recessus labyrinthi in the 
Dipnoi is very interesting. Retzius was unable to find this 
organ, as he examined badly preserved specimens. It is now 
known that the ductus and saccus endolymphaticus of Neocera- 
todus resemble the same structures in the Ganoidei. Burne 
(13) writes as follows: 
The saccus endolymphaticus is a capacious pear-shaped vesicle with 
bluntly rounded apex, situated to the mesial side of the space enclosed 
by the anterior semicircular canal, with its apex inclined somewhat 
forward. It is supported by a sheet of membrane (? dura mater) 
within which wedged in between the apices of the two sacci endolym- 
phatici is a large vessel, probably a vein. The lower end of the saccus 
endolymphaticus bends slightly forward along the sinus anterior utri- 
culi and gradually narrows to form the ductus endolymphaticus which 
crosses the utricle near its anterior end and opens by a funnel shaped 
mouth into the anterior extremity of the sacculus. These organs show 
a great resemblance to the same organs figured by Retzius in the 
sturgeon. 
Protopterus, which was examined by Burckhardt, (’93), differs 
greatly from the above-described animal. The saccus endolym- 
phaticus is here an inflated bag lying in the cavum cranii and 
giving rise to many tube-like diverticule which are filled with 
calcareous matter. The organ covers nearly the whole of the 
sinus rhomboidalis and extends caudally as far as the root of 
the first pair of spinal nerves. ‘The saccus of the one side does 
not communicate with that of the other. 
The first description of the conditions in the Urodela was pub- 
lished by Calori (50). He found between the bulbae auditoriae 
of the axolotl a sac containing calcareous matter, extending 
from the lobi optici over the corpora quadrigemina and the 
medulla oblongata. He connected this structure with the 
labyrinth, but did not explain the relations in detail. Hasse 
proved that this organ represents the two sacci endolymphatici, 
which are here amalgamated. In Triton, Hasse found condi- 
