BULLETIN OF THE UNITED STATES FISH COMMISSION. 
244 
receive a sufficiently circumscribed stimulation. It is unnecessary to follow the 
argument in detail, for the experiments which I shall describe shortly show conclu- 
sively that when the sapid substance is brought into contact with these organs or 
very near to them the stimulus is accurately and very promptly localized, and in fact 
some of the fishes studied habitually find their food by this very power, the gusta- 
tory stimulus calling forth an immediate reflex movement toward the point stimu- 
lated. It is probable that the local sign is not given by the gustatory (communis) 
nerves, but by the accompanying tactile (general cutaneous) nerves of the corre- 
sponding - cutaneous area (which general cutaneous nerves Merkel, curiously enough, 
denies to the fishes altogether, whereas, in fact, they are plentifully supplied to all 
parts of the skin), though my experiments do not decisively answer this question. 0 
Weak stimuli, especially when uniformly diffused through the water, are, it is true, 
not at all localized; but strong stimuli are unquestionably localized by one method 
or another. 
In fact, Merkel agrees with Jobert that the terminal buds of the outer skin are 
tactile in function. This is based largely on the erroneous belief, referred to above, 
that there are no free tactile nerve endings in the skin of fishes, and also on the 
observed tactile sensibility of the barblets and other parts of the body known to be j 
most plentifully supplied with terminal buds. But I have shown that all of these 
parts of the body receive, in addition to communis nerves for the specialized sense 
organs, a most liberal general cutaneous innervation foi tactile sensibility; and the 
experiments which follow go to show practically that these two functions commonly 
cooperate in setting oft' the reflex of seizing food, though they may be experiment- 
ally isolated. 
Merkel now proceeds to carry his argument to its logical conclusion (and like- 
wise to a reductio ad absurd am ) by denying the gustatory function to all terminal 
buds, even those within the mouth supplied by the glossopharyngeal nerve, of all 
vertebrates below the Mammalia. 
He finally concludes that both the neuromasts of the lateral-line system and the 
terminal buds are tactile organs, the buds being the more delicate; but if these are 
deficient, then the neuromasts may be elevated to a more delicate functional value; 
both of which conclusions, in the light of our present knowledge, illustrate the dangers 
attending an attempt to determine function on the basis solely of observed structure, 
without adequate physiological control. 
The general works contain numerous references to the subject, but usually 
chance observations or speculative conclusions. Gunther says, under the caption 
“ Organ of taste”: 
Some fishes, especially vegetable feeders, or those provided with broad molar-like teeth, masticate 
their food; and it may be observed in carps and other cyprinoid fish that this process of mastication 
frequently takes some time. But the majority of fish swallow their food rapidly and without mastica- 
tion, and therefore we may conclude that the sense of taste can not be acute. The tongue is often 
entirely absent, and even when it exists in its most distinct state it consists merely of ligamentous or 
cellular substance, and is never furnished with muscles capable of producing the movements of exten- 
sion or retraction, as in most higher vertebrates. A peculiar organ on the roof of the palate of cypri- 
noids is perhaps an organ adapted for perception of this sense; in these fishes the palate between and 
below the upper pharyngeal bones is cushioned with a thick, soft, contractile substance, richly supplied 
with nerves from the Nervi vagus and glossopliaryngeus. 
«On this point, see the further experiments recorded in the Addendum, pp. 270-271. 
