SENSE ORGANS OF AMIURUS. 373 



labyrinth — I prefix, for the sake of completeness, a few particulars 

 as to the olfactory organ and eye. 



With respect to the former, Amiurus differ very slightly from 

 Silurus glanis. Like most Teleosts the nasal sacs communicate with 

 the outside by two apertures, which are separated by the whole of 

 the length of the roof of the sac, as much as 12 mm. in specimens 

 of moderate size. The anterior aperture is somewhat oblique and 

 prolonged into a short tube of 2 mm. in diameter, while the poste- 

 rior, twice as wide, is overhung by .the nasal barblet which originates 

 immediately in front of it. In connection with the roof of the sac are 

 both the nasal and adnasal or antorbital bones. The apertures are 

 situated in the same sagittal plane, but after the removal of the roof, 

 it is evident that the sacs themselves converge backwards. (Fig. 12 

 PL I.) A high epithelium clothes the roof and the posterior part of 

 the floor of the sac. The rest of the floor is elevated into the 

 Schneiderian folds which are disposed on either side of a median 

 raphe. On each side of the raphe there are fifteen to sixteen 

 of these arranged in a somewhat fan-like fashion. Immediately be- 

 hind and underneath the folds is the olfactory bulb from which 

 the short nerve fibres distribute themselves to the neuro-epith- 

 elium. 



The small size of the eye in Amiurus renders it a somewhat un- 

 favorable subject for investigation. As far as concerns the disposi- 

 tion of the muscles of the eye, the retrobulbar tissue and the coats 

 of the optic nerve, I have not observed anything depai'ting from the 

 normal condition of affairs. The sclerotic coat is destitute of bone, 

 is entirely fibrous in the neighbourhood of the entrance of the optic 

 nerve, but becomes cartilaginous forwards until it passes into the 

 substantia propria cornece. A comparatively thick layer of subcon- 

 junctival tissue separates this from the external epithelium. 



I have not satisfied myself of the presence of any rudiment of the 

 chorioideal gland ; but the existence of a rudimentary pseudobranchia 

 renders worthy of more careful investigation the distribution in the 

 eye of the arteria ophthalmia/ magna. The argentea is well developed, 

 especially in the iris, but there is no tapetum. Like Anguilla, which 

 Amiurus further resembles in the small size of the eye, the pigmen- 

 tary epithelium of the retina is extremely thick, as much so as the 



