11, ELECTRORECEPTION
553
diagrams of the brains of several fish with and without electrosensory systems. Neuroanatomy of the cerebellum of fish has recently been reviewed
by Nieuwenhuys ( 1967) and Schnitzlein and Faucette ( 1969). The trout,
Salmo fario, may be taken as a generalized teleost (Fig. 38A). The
buffalo fish Curpiodes is a sucker, a bottom feeding relative of the carp.
It has a very developed gustatory system and correspondingly the vagal
lobes are very enlarged, but otherwise its brain resembles that of the
trout (Figs. 38B and C). The squirrelfish has very large eyes, and its
optic tecta are quite enlarged (Fig. 38D). The stargazer has an electric
organ but is not known to have electroreceptors. Its brain is quite similar
to that of the trout except for the smaller cerebellum and the very large
oculomotor nerves that innervate the electric organ (Fig. 38E). The
cerebellum is also implicated in the control of movement, and the small
size in the stargazer correlates with its sedentary mode of life. It generally
lies buried in the sand with only its small eyes protruding and waits until
prey comes near enough to gulp down.
The elasmobranchs are divided into two main lines, the sharks and
the batoids including skates, electric rays, stingrays, and guitarfish. A
wide but similar range of cerebellar development is seen within each
line ( Ariens-Kappers et ul., 1936; Schnitzlein and Faucette, 1969). The
brain of a ray that has a simple cerebellum is shown in Fig. 38F. This
cerebellum is still considerably larger than that of the trout. In the guitarfish and stingray, the corpus is highly convoluted and greatly enlarged.
No data are available for correlation of electrosensory function with
cerebellar enlargement within the elasmobranchs. There is some tendency
for more elaborate cerebella to be found in more actively swimming
species, but whether this increased development represents increased sensory or control requirements is not yet clear.
The cerebellum of the catfish Amiurus is greatly enlarged compared
to that of the teleosts without an electrosensory system (Fig. 38G). The
cerebellum of gymnotids is similarly enlarged ( Fig. 38H). The extreme
case of enlargment of the cerebellum is in the mormyrids in which it
constitutes most of the brain (Figs. 381 and J ) . The cerebellum in mormyrids is extraordinarily specialized cytologically ( Nieuwenhuys and
Nicholson, 1969a,b; Kaiserman-Abramoff and Palay, 1969). Just as
increase in optic tecta or vagal lobes implies a role in increased visual or
gustatory sensitivity, hypertrophy of the cerebellum in fish with electrosensory systems implies a role in electroreception. There are corresponding increases in the afferent pathways from lateral line inputs to at least
the valvulae of the cerebellum (Berkelbach van der Sprenkel, 1915;
Nieuwenhuys and Nicholson, 1969a; Szabo, 1967).
There is limited physiological evidence for involvement of the cerebel-
553
diagrams of the brains of several fish with and without electrosensory systems. Neuroanatomy of the cerebellum of fish has recently been reviewed
by Nieuwenhuys ( 1967) and Schnitzlein and Faucette ( 1969). The trout,
Salmo fario, may be taken as a generalized teleost (Fig. 38A). The
buffalo fish Curpiodes is a sucker, a bottom feeding relative of the carp.
It has a very developed gustatory system and correspondingly the vagal
lobes are very enlarged, but otherwise its brain resembles that of the
trout (Figs. 38B and C). The squirrelfish has very large eyes, and its
optic tecta are quite enlarged (Fig. 38D). The stargazer has an electric
organ but is not known to have electroreceptors. Its brain is quite similar
to that of the trout except for the smaller cerebellum and the very large
oculomotor nerves that innervate the electric organ (Fig. 38E). The
cerebellum is also implicated in the control of movement, and the small
size in the stargazer correlates with its sedentary mode of life. It generally
lies buried in the sand with only its small eyes protruding and waits until
prey comes near enough to gulp down.
The elasmobranchs are divided into two main lines, the sharks and
the batoids including skates, electric rays, stingrays, and guitarfish. A
wide but similar range of cerebellar development is seen within each
line ( Ariens-Kappers et ul., 1936; Schnitzlein and Faucette, 1969). The
brain of a ray that has a simple cerebellum is shown in Fig. 38F. This
cerebellum is still considerably larger than that of the trout. In the guitarfish and stingray, the corpus is highly convoluted and greatly enlarged.
No data are available for correlation of electrosensory function with
cerebellar enlargement within the elasmobranchs. There is some tendency
for more elaborate cerebella to be found in more actively swimming
species, but whether this increased development represents increased sensory or control requirements is not yet clear.
The cerebellum of the catfish Amiurus is greatly enlarged compared
to that of the teleosts without an electrosensory system (Fig. 38G). The
cerebellum of gymnotids is similarly enlarged ( Fig. 38H). The extreme
case of enlargment of the cerebellum is in the mormyrids in which it
constitutes most of the brain (Figs. 381 and J ) . The cerebellum in mormyrids is extraordinarily specialized cytologically ( Nieuwenhuys and
Nicholson, 1969a,b; Kaiserman-Abramoff and Palay, 1969). Just as
increase in optic tecta or vagal lobes implies a role in increased visual or
gustatory sensitivity, hypertrophy of the cerebellum in fish with electrosensory systems implies a role in electroreception. There are corresponding increases in the afferent pathways from lateral line inputs to at least
the valvulae of the cerebellum (Berkelbach van der Sprenkel, 1915;
Nieuwenhuys and Nicholson, 1969a; Szabo, 1967).
There is limited physiological evidence for involvement of the cerebel-