30 
IOWA ACADEMY OF SCIENCES. 
canals, or at least any more than as rudiments. It was very 
early recognized that two distinct forms of ear were to be found 
in the group of Cyclostomata, the one found in the Myxine and 
the other in the Lampreys. Muller^ first gave any adequate 
description of the ear of Myxine. Previously Anders Retzius^*^ 
had given a very meager description. Ketel attempted to show 
that the ear of Myxine is genetically related to that of higher 
vertebrates through the ear of Petromyzon as a connecting 
link. Unfortunately he failed to recognize the existence of 
semicircular canals in the ear of Myxine, considering the mem- 
branous vestibule as merely a ring. Ibsen“ had in 1846 recog- 
nized a semicircular canal in Myxine and two ampullae. 
Ketel considered the Cyclostome ear as in an arrested stage 
of evolution, and that it really represented an ancestral condi- 
tion of the Vertebrate ear. He sought for traces of the third 
or horizontal canal in Petromyzon, and believed he found it in 
a sense organ connected with the crista acustica of the anterior 
canal. The cochlea he found represented in the “ sackartiger 
Anhang” of the membranous labyrinth. Ketel failed to com- 
pletely homologize the Cyclostome ear with that of the Verte- 
brate type, because he did not recognize the existence of 
semicircular c anals in Myxine, and further, because, working 
from the higher types downward, he had not grasped the idea 
of the fundamental form of the auditory organ. Gustav 
Retzius^^ in 1881 recognized the existence of a single semi- 
circular canal in Myxine; but he did not agree with Ketel as to 
the relationships of the ear of the Cyclostomata. It remained 
for Ayeis^-^ in 1892 to establish beyond question the rank of the 
Cyclostome ear. Starting with the idea that the Vertebrate 
auditory organ is composed of modified sense organs of the 
lateral line system, he shows almost beyond question that the 
Cyclostome ear is not a degenerate structure, but rather repre- 
sents an ancestral type. According to this ioterpretalion, we 
recognize in the Vertebrate ear two originally distinct parts, 
an anterior utriculus and a posterior sacculus, with which, aM 
forming a part of, are a number of canals. The ear of Myxine 
9 Loc. cit. 
10 Ytterligare Bidrag till anatomien af Myxine glutinosa. Kongl. Vet.-Altad. 
Handl. Stockholm, 1824. 
11 Anatomiske Undersogelser over Orets Labyrinth, afsluttet af Forgattern i 1846. 
i2Das Gehororgan der Wirbelthiere I, Stockholm, 1881. 
Invertebrate Cephalogenesis, II. A Contribution to the Morphology of the Verte- 
brate Ear, with a Reconsideration of its Functions. Journal of Morphology, Vol. VI, 
Nos. land 2. 1892. 
