IOWA ACADEMY OP 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 Keieh, 
in 1872.' His predecessors had assumed that the auditory organ 
of the Cyclostomata 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 were 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 
Muller^ in 1636 discovered the semicircular canals in the ear of 
Petromyzon, and that they were only two in number. DumeriP 
in 1800 claimed to have found the canals, but his statements 
are extremely vague. Other observers, PohP, Weber^, Blain- 
viile®, Rathkee and BrescheP, had denied the existence of the 
1 Ueber das Gehorogan der Oyclostomen.— Hasse Anat. Studien, 1873. 
2Ueber den eigenthumliclien Ban des Gehororgans bei den Oyclostomen. Fortsetz 
d Vergl. Anat. d. Myxinoiden in Ahh d. K. Almd. d mssen. Berlin, 1836. 
3 Anatomie des Lamproies Memoires d anatomie compmxe. Paris, 1800. 
^Expositis generalis anatomica organi auditiis per classes animalium. Vindo- 
bonae, 1818. 
5De aure et auditu hominis et animalium. Leipzig, 1830. 
6De I’organisation des animaux ou Principes d’auatomie comparee. Paris, 1833. 
7Bemerkungen uber den inneren Bau der Pricke. Danzig, 1836. 
8 Recherches anatomiques et physiologiques sur I’organe de I’ouie des poissons. 
Acad, des Sci Savans Eirangers. 1838. 
