374 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



rest of the retina, but unlike Anguitta there are no retinal vessels. 

 So far as I have observed the lens ; its capsule, campanula Halleri and 

 processus falciformis offer no exceptional features. 



AUDITORY ORGAN. 



In many respects the labyrinth of Amiurus resembles that of the 

 Cyprinoids. The pars superior and inferior are equally widely sepa- 

 rated, and while the connecting narrow but thick-walled ductus sac- 

 culo-utricularis is very distinct, the pars inferior lies largely behind 

 the pars superior. The latter is especially distinguished by the large 

 size of the recesstcs utriculi, and of the contained macula and otolith 

 (lapillus), Fig. 9, PI. I. Unlike the pars inferior it lies comparatively 

 free in the cranial cavity, except for certain parts of the semi-circular 

 •canals. The wall of the skull opposite the fovea rec. utr. is extremely 

 thin, but over against the thin- walled utriculus is much thicker. 

 Where the ductus sacculo-utricularis opens into the pars inferior, the 

 latter also looks freely into the cranial cavity. At this point the 

 fovea; sacculi, which are hollowed out on the upper surface of the 

 basi-occipital bone, are separated from each other by a median crest, 

 somewhat wider anteriorly, where the anterior tips of the sacculi 

 (processes of Comparetti) 1 diverge forwards into small recesses of the 

 prootics. To this crest the wall of the labyrinth is attached, as repre- 

 sented in Figs. 8 and 9, PI. VI.; the relationship to it of the posterior 

 branches of the auditory nerve is seen from the same figures. Fur- 

 ther back the fovea; are separated by the median cavum sinus im- 

 paris ; whose floor is hollowed out in the basi-occipital, but whose 

 walls and roof are furnished by the ex-occipital*. The relationship 

 of these cavities may be gathered from Fig. 15, PI. IV., which repre- 

 sents a frontal section through the head of a young fish of 3-4 ctm., 

 and from the figures on Plate VI. It will be seen that the ex-occipi- 

 tals also form the lateral wall and roof of each. fovea sacculi, and that 

 especially the lagena; cochlea; are lodged in these bones. 



Figs. 9 and 10, PI. 1, represent the medial and lateral aspects of the 

 labyrinth. The relative position of the lagena cochlea;, and sacculus, 

 and of the contained macules acustica;, may be better seen from Fig. 15, 

 PI. IV. The otoliths which rest on the macula; acusticm of the 

 recessus utriculi, lagena cochlear, and sacculus respectively, and which 



1 Hasse : — Ai.atomische Studien I., 592. 



