242 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
be similar to that of taste buds within the mouth, viz, the perception of chemical 
stimuli. 
In 1870 the same author (F. E. Schulze, ’70) made a further important contri- 
bution to the problem of the terminal buds by the demonstration that they differ 
structurally from all neuromasts, or organs of the lateral-line system. The neuro- 
masts are commonly sunken below the skin in canals, tubes, or pits, but in some 
cases they are strictly superficial and resemble in external form the terminal buds 
very closely — a feature which led Lcydig (’51, ’79, ’94) and others to assume that the 
two classes of organs are mere varieties of a common type. Schulze showed that 
the neuromasts can in all cases be differentiated from the terminal buds by the fact 
that their specific sensory cells (pear cells) extend only part way through the 
sensory epithelium and fail to reach the internal limiting membrane, while in the 
terminal buds both specific sensory 
cells and supporting cells pass through 
from external to internal limiting mem- 
brane. 
This distinction was confirmed by 
Merkel (’80), who, with curious incon- 
sistency, while recognizing the struc- 
tural dissimilarity of the two classes of 
organs, nevertheless, as we shall see 
below, ascribes to both essentially the 
same function, touch. This matter 
was put to the decisive test in my 
contribution on Ameiurus (’01), a type 
which possesses both terminal buds 
and neuromasts in great abundance 
and diversity of forms. Schulze’s 
contention is supported both by the 
structure of the organs and by their 
innervation, for I have shown that 
all neuromasts of whatever form are 
innervated by acustico-lateralis nerves from the tubereulum acusticuin of the brain, 
while all terminal buds, whether within the mouth or in the outer skin, are inner- 
vated by communis nerves related centrally to a single center within the brain. 
This center is bilobed, the lobus vagi receiving most of the communis fibers from 
the mouth cavity by way of the vagus and glossopharyngeus and the lobus facialis 
the communis fibers from the terminal buds of the outer skin by way of the facial 
nerve (cf. fig. 1). 
Similar terminal buds have been found in the outer skin of many species of 
Teleostomes and in Cyclostoines, but, so far as certainly known, nowhere else among 
vertebrates (save on the lips of some other classes). Their distribution among the 
fishes is very irregular, being most abundant among the siluroids, eyprinoids, 
ganoids, and cyclostoines, in general bottom fishes of sluggish habit, often living 
in mud and rarely belonging to the predaceous types which find their food chiefly 
by the sense of sight. The following list of fishes which have been shown to possess 
Fig. 1. — Dorsal view of the brain of the yellow cat-fish (Lap- 
tops olivaris Rat). The olfactory bulbs with most of their 
crura have been removed, also the membranous roof of the 
fourth ventricle, exposing the facial and vagal lobes. This 
v ventricle is bounded behind by a transverse ridge contain- 
ing the commissura infima Halleri and the commissural 
nucleus of Cajal. x2. 
