IOWA ACADEMY OF SCIENCES. 29' 



HOMOLOGIES OF THE CYCLOSTOME EAR. 



BY H. W. NORRIS, 



The ear of the Cyclostomata has until recently been consid- 

 ered so peculiar as to render it difficult to explain its relations 

 to the typical Vertebrate ear. Then again, the diversity of 

 structure in the auditory organ of the Cyclostomes themselves 

 renders the task of homologizing the various parts somewhat 

 uninviting. 



Our exact knowledge of the structure and relations of the 

 ear of the Cyclostomata begins with the researches of KeteP, 

 in 1872. His predecessors had assumed that the auditory organ 

 of the Cyclosttmata was a thing sui generis, hence most of their 

 observations were defective. Ketel was the first to attempt 

 to find a fundamental type of the vertebrate ear. While the 

 results of his studies in that direction did not find ready accept- 

 ance, nevertheless, in the light of most recent investigations, 

 we see that his conclusions Vvcre essentially correct. In the 

 light of zoological knowledge twenty years later, his opinions 

 would have seemed not only reasonable, but they would have 

 been considerably modified from their original form. Johannes 

 Mtiller^ in 1636 discovered the semicircular canals in the ear of 

 Petrcmyzon, and that they were only two in number. DumeriP 

 in 1800 claimed to have lound the canals, but his statements 

 are extremely vague. Other observers, PuhP, Weber-^, BLain- 

 viile^ Rathkb' and Breschet^ had denied the existence of the 



1 Ueber das Gehorogan der Oyclostomen.— Hasse Anat. Studien, 1872. 



2 Ueber den eigeutbumlichen Ban des Gehororgans bei den Oyclostomen. Fortsetz 

 d Vergl. Anat. d. Myxinoidcn in Ahh d. K. Akad. d Wissen. Berlin, 18315. 



3 Anatomie des Lamproles Memoirctt d anatomie comparee. Paris, 1800. 

 lExposItis generalis anatomica organi auditus per clatses auimalium. Vindo- 



bonae, 1818. 



5De aure et auditu hominis et animaliuru. Leipzig, 1820. 



6De I'organisation des auimaux ou Principes d'anatomie comparee. Paris, 1822. 



7Bemerkungen uber den inneren Bau der Pricke. Danzig, 1826. 



SEecherches anatomiques et pbysiologiques sur I'organe de I'ouie des poissons. 

 Acad, des Sci Savmis Etrangcrs. 1838. 



