SENSE ORGANS OF AMIURUS. olor 
labyrinth—I prefix, for the sake of completeness, a few particulars 
as to the olfactory organ and eye. 
With respect to the former, Amiwrus 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. 1.) 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 departing 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 cornee. 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 ophthalmica 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 
