62 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
isolated sense-cells and nerve-endings in various parts of 
its internal epithelium; but is very badly provided with. 
more definite ‘‘ sense organs.’ It has no true eyes—for 
the little brightly-coloured dots or “ ocelli”’ placed along 
the margins of the apertures (Pl. I.), and formed of a 
group of modified ectoderm cells, supplied by a nerve and 
imbedded in a mass of red and yellow pigment (PI. IV., 
fig. 8), can scarcely be called such; and it certainly has 
no ears or otocysts. The tentacles are not very efficient 
tactile organs, and the thin expanded margins of the 
branchial and atrial siphons are apparently the most 
sensitive parts of the body. 
But there is a curiously-curled projection, the Dorsal 
Tubercle (Pl. IL., fig. 7, d.t.), placed at the front of the 
dorsal lamina, in the preoranchial zone, near the entrance 
to the branchial sac, which may possibly be an organ for 
testing, by smell or taste, the quality of the water drawn 
in through the branchial aperture. This organ has a 
narrow slit which leads by means of a ciliated funnel into 
a delicate non-ciliated tube, and this can be traced back 
for a distance of several centimetres to a glandular mass, 
the neural gland, formed of tubules lined by small cubical 
cells, lying imbedded in the connective tissue immediately 
underneath the brain (see 2. gl., fig. 6, Pl. IL.). 
Hence, it has been suggested that the supposed olfactory 
organ is merely the complicated opening of the duct from 
the neural gland, and that this gland probably corresponds 
to the hypophysis cerebri or pituitary body, which is 
found in all Vertebrata, from fishes up to man, attached 
to the infundibulum on the lower surface of the brain. It 
is probable that both views are partly right, and that 
therefore the duct of the pituitary gland in the Ascidian, 
opens into a sense organ placed on the roof of the mouth. 
Sensory cells have been found amongst the ciliated 
