9. THE MAUTHNER CELL
339
to the author many years ago by A. R. Ness of University College
London. (The author is indebted to Mr. Ness for much information on
these birds.) Many species of teleost fish live, or spend much of their
time, in relatively shallow water, and as such are the natural prey of
most species of fish-eating birds. Some birds pick or scoop up fish
(shearwaters, frigate birds, and white pelicans), and here we may suppose that optical stimuli to the fish may be especially important, more
so than vibrational ones, in contributing to a startle-response. This
would apply too in the case of swimming birds which dive from the
surface (cormorants, auks, and penguins), but there could also be an
important effect on the fish from the shock wave. However the group
of birds against which the startle-response would seem to offer the
greatest protection must surely be the diving or plunging birds,
both those which pick up with the beak (kingfishers, terns, gannets,
Tropic Birds, and brown pelicans) and with the feet (osprey). It can
be calculated that the minimum time which elapses between a diving
bird hitting the water surface (and thus providing the mechanicaland probably optical-stimulus) and arriving at the level of a fish not
far from the surface, would be a few tens of milliseconds. The interval
between mechanical stimulation (of the vestibular system) and the
early development of the Mauthner reflex movement would be about
the same. The reflex response seems to move the fish just a few centimeters away from its original position (usually it finishes u p to one side
rather than ahead or behind), but this could be enough to cause the
bird to miss its target.
Some casual observations by the author on the responses of freely
swimming goldfish to surface splashing suggest that the startle-response
is usually immediately followed by escape swimming; the initial characteristic swiveling movement, the presumed Mauthner reflex, was however readily distinguishable, and to the observer there seems to be
a clearly detectable brief lapse of time before true swimming begins.
The latter might well require some orienting cues. The startle-response
serves simply to put the fish slightly away from the position it was in
when the bird first sighted it and made its dive. On this basis it
would be immaterial which way the fish moved, and all that we have
said about the Mauthner cell reflex implies that it would not matter
which cell fired first. This proposition remains to be proved. It could
be that optical stimuli, which are obviously capable of influencing the
Mauthner cells, might contribute to an orienting startle-response if
they originated sufficiently to one side or-if
derived from moving
sources-they produced some appropriate retinal image ( cf. Rodgers
et al., 1963). This possibility could work to advantage against the un-
339
to the author many years ago by A. R. Ness of University College
London. (The author is indebted to Mr. Ness for much information on
these birds.) Many species of teleost fish live, or spend much of their
time, in relatively shallow water, and as such are the natural prey of
most species of fish-eating birds. Some birds pick or scoop up fish
(shearwaters, frigate birds, and white pelicans), and here we may suppose that optical stimuli to the fish may be especially important, more
so than vibrational ones, in contributing to a startle-response. This
would apply too in the case of swimming birds which dive from the
surface (cormorants, auks, and penguins), but there could also be an
important effect on the fish from the shock wave. However the group
of birds against which the startle-response would seem to offer the
greatest protection must surely be the diving or plunging birds,
both those which pick up with the beak (kingfishers, terns, gannets,
Tropic Birds, and brown pelicans) and with the feet (osprey). It can
be calculated that the minimum time which elapses between a diving
bird hitting the water surface (and thus providing the mechanicaland probably optical-stimulus) and arriving at the level of a fish not
far from the surface, would be a few tens of milliseconds. The interval
between mechanical stimulation (of the vestibular system) and the
early development of the Mauthner reflex movement would be about
the same. The reflex response seems to move the fish just a few centimeters away from its original position (usually it finishes u p to one side
rather than ahead or behind), but this could be enough to cause the
bird to miss its target.
Some casual observations by the author on the responses of freely
swimming goldfish to surface splashing suggest that the startle-response
is usually immediately followed by escape swimming; the initial characteristic swiveling movement, the presumed Mauthner reflex, was however readily distinguishable, and to the observer there seems to be
a clearly detectable brief lapse of time before true swimming begins.
The latter might well require some orienting cues. The startle-response
serves simply to put the fish slightly away from the position it was in
when the bird first sighted it and made its dive. On this basis it
would be immaterial which way the fish moved, and all that we have
said about the Mauthner cell reflex implies that it would not matter
which cell fired first. This proposition remains to be proved. It could
be that optical stimuli, which are obviously capable of influencing the
Mauthner cells, might contribute to an orienting startle-response if
they originated sufficiently to one side or-if
derived from moving
sources-they produced some appropriate retinal image ( cf. Rodgers
et al., 1963). This possibility could work to advantage against the un-