400 



of one being as it were guarded by the recessus utriculi and its macula, 

 that of the other in a similar way by the macula neglecta. Whether 

 the independent passages by which these utriculi communicated with 

 the saccule coalesced to form the single canalis utriculo-saccularis of 

 typical Vertebrates or whether the posterior one became obliterated 

 is an open question. This dilatation in Ceratodus suggests a closed 

 posterior utriculo-sacculine passage, except for the fact that the 

 macula neglecta lies upon its anterior lip and not upon the posterior 

 as it does in the case of the posterior utriculo-sacculine passage in 

 sharks. 



In neither Ceratodus nor Protopterus was Eetzius able to 

 describe the condition of the ductus or Saccus endolymphaticus. — 

 In the present specimen these were well preserved and no doubt their 

 condition is characteristic of the Dipneusti (Figs. 1, 2, SEDL. DEDL.). 



They show a great resemblance to the same organs as figured by 

 Eetzius in the Sturgeon (PL IV, fig. 1, 2), though they are larger 

 and more fully developed than in specimens of the ear of this Fish in 

 the Museum of the K. College of Surgeons. 



The Saccus endolymphaticus is a capaceous 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 some 

 what forward. It is supported by a sheet of membrane ( '? dura mater) 

 within which, wedged in between the apices of the two sacci endo- 

 lymphatici is a large vessel, probably a vein (V.). 



The lower end of the saccus endolymphaticus bends slightly for- 

 ward along the sinus anterior utriculi 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 (fig. 1 and 2). The wall of. the saccus endolymphaticus 

 is yellow and shrivelled very much as it is in the Sturgeon. 



Abgeschlossen am 18. März 1913. 



Weimar. — Druck von R. Wagner Sohn. 



