OLFACTORY ORGANS. 189 
and while some fishes have been proved to hear, others have given 
negative results. With the terrestrial vertebrates the sound percipient 
functions of the ear are beyond a doubt, while they still retain their 
equilibrational use. The sound waves strike the tympanic membrane, 
are carried across the middle ear by the auditory ossicles, and set the 
perilymph in motion and thus affect the parts of the membranous 
labyrinth. 
Organs of Taste. 
The sense of taste is resident in groups of cells known as taste buds. 
These differ morphologically from the lateral line organs in having 
each sensory cell extend the depth of the bud, ending at the basal mem- 
brane, while the majority of the supporting cells are on the outer side of 
the bud. Each sense cell bears a short, bristle-like percipient struc- 
ture on its free end, while the basal end is embraced by the fibrillz of the 
nerve. According to the accounts of the development the taste buds 
are derived from the entoderm, the only case apparently established 
for the origin of sense organs except from the ectoderm. In the higher 
vertebrates the organs are restricted to the cavity of the mouth where 
(mammals) they occur on the tongue, especially on and near the cir- 
cumvallate papilla, on the soft palate and on the epiglottis. In the 
fishes the distribution is much wider, for they are found in the pharynx, 
on the gills, and in many species on the surface of the body, even upon 
the tail. The barbels about the mouth of many forms are richly 
supplied with these organs. 
The taste organs are supplied by different nerves. Apparently 
those of mammals are supplied by the chorda tympani and the lingual 
branch of the ninth nerve. In the fishes those of the pharyngeal 
region are supplied by the post-trematic branches of the glossopharyn- 
geal and vagus; those of the mouth by the palatine and mandibular 
branch of the seventh; while those on the head of teleostomes are 
supplied by the ophthalmic and maxillary branches of the fifth; and 
those of the trunk by the nerve of Weber (p. 173), formed by fibres 
from the seventh and sometimes of the tenth nerves. 
Olfactory Organs. 
While the senses of smell and taste are closely associated physiolog- 
ically, being what might be called the chemical senses, the organs con- 
