258 BEATRICE WHITESIDE 
sich begibt. Es ist dies der Ductus endolymphaticus oder Aquaeductus 
vestibuli mit dem Saccus endolymphaticus von dem wir wissen, dass 
es eine blind geschlossene Ausstuelpung des Labyrinthblaeschens 
gegen das Cavum cranii hin darstellt. 
Hasse found this structure in Myxine and Petromyzon. In 
these animals the organ starts from the inner ear, or saccus com- 
munis, goes through the apertura aquaeductus vestibuli, and 
ends in the cavum cranii with a slight enlargement. The dilated 
end is filled with calcareous matter. 
The Elasmobranchii have been investigated by Hasse and 
Retzius. In these animals the ductus endolymphaticus is a 
very noticeable structure opening to the exterior. In Chimaera 
it runs from the sacculus almost straight to the top of the head. 
In the sharks it expands just beneath the opening, into a saccus, 
either a small one as in Scyllium or a somewhat larger one as in 
Acanthias and Aquatina. ‘This last-named animal is, in this 
respect, a transition form leading to Raja, in which the ductus 
dilates and forms a large sac lying almost horizontally under the 
skin. Trygon and Torpedo have a formation similar to that 
in the sharks. In all cases the ductus as well as the saccus is 
filled with lime crystals which run out when the skin is pressed 
in the neighborhood of the opening. This is also the case in 
living animals. 
Retzius examined five Ganoidei, namely, Acipenser, Lepi- 
dosteus, Amia, Polypterus, and Calamoichthys. In Acipenser 
the ductus endolymphaticus runs upward from the sacculus and 
expands beside the upper end of the utriculus into an oblong 
vesicle which adheres to the dura mater. In Lepidosteus and 
Amia the relations are similar. Polypterus and Calamoichthys, 
which are particularly interesting on account of their relation- 
ship to the Crossopterygii, do not deviate either. 
The. question whether a small duct, which in the Teleostei 
starts from the sacculus and leads upward a short distance only 
to end blindly without an enlargement, is to be looked upon as 
the ductus endolymphaticus has been much discussed. Krause 
(01) denies this and founds his opinion on the manner of develop- 
ment. Wiedersheim (’09) agrees with him. On the other hand, 
