IV. On the Auditory Labyrinth of Orthagoriscus Mola L.* 
By Professor D’Arcy W. THompson. 
A LarGE Sunfish, caught in the Firth of Forth, came lately into my possession. It 
measured from snout to tail 1.35 m., and from the tip of the dorsal to that of the 
ventral fin 1.73 m. The anatomy of the fish is for the most part well known, but 
the auditory organ seems to have escaped critical examination ; and Rerzrus in his 
great work notes with regret his inability to obtain a specimen. 
Excluding one or two cursory notices, the only account of the organ that I 
know of, is that by Hartine:+ but Harrrne enters into no details whatever 
regarding the structure of the vestibule, merely describing the position of the 
labyrinth in the auditory capsule, and giving some of its dimensions, and also calling 
attention to the presence of three semicircular canals, instead of two, as had formerly 
been described. 
The auditory labyrinth of Orthagoriscus is very peculiar, and differs more or 
less from that of all other Teleostean fishes. It hangs suspended by webs of delicate 
connective tissue within a wide space, continuous with the brain-cavity, very much 
as in Chimaera, according to Rerzrus’ description. A single vertical pillar of cartil- 
age passes down across this space, within the arc of the horizontal canal. (In 
Hartine’s specimen another passed within the are of the anterior vertical canal.) 
After removal of the membranous labyrinth no distinct grooves or impressions 
remain in the cartilage capsule to indicate the former position of the parts within it. 
Fig. 1. 
_ Fig. 1. Auditory labyrinth of Orthagoriscus Mola within its cavity. The connective tissue filaments are omitted. 
@.8.C., p.8.¢., anterior and posterior semicircular canals. VII., X., Isp., nerve foramina. 
* Reprinted from the Anatomischer Anzeiger. III. Jahrgang, Nr. 4 und 5, 1888. 
t “Sur ? Orthayoriseus Ozodura,” Kon. Ak. Wet. Amsterdam, XI., 1868. 
