340
J. DIAMOND
welcome attention of birds like the herons and bitterns, which catch
fish from a wading position.
The fact that birds which prey on fish do so successfully, and improve their performance as they grow to maturity, does not invalidate
the probable importance of the startle-response as an avoidance reaction
particularly developed to help shallow-living fish escape such birds.
It is significant that the “Mauthnerian apparatus” is absent or poorly
developed in tailIess fish, in almost all species living mostly at the
bottom, and in those showing eellike (anguilliform) movements; it is
interesting too that Mauthner cells are absent in anuran tadpoles with
small tails and most prominent in those with large ones, while on
metamorphosis of these species into tailless adult forms the Mauthner
cells atrophy altogether ( Stefanelli, 1951). The association of the Mauthner cell with the tail however has tended in the past to strengthen a
belief that the role of the cell is in swimming. We have rejected this
view in the preceding pages. The important points are the biological
environment of the tailed animals which have Mauthner cells, and
the characteristics of the circuitry of which the Mauthner neurons are
a part. Aquatic predators as well as birds may to some extent be put at
a disadvantage by the existence of the startle-response. However, it
may be that in this instance the lateral line system may be more important, and only in some species do fibers of the (anterior) lateral line
nerve extend to the Mauthner cells [Aronson (1963)-see also the
other origins of inputs to the Mauthner cell (Fig. 4)].
D. The Functions of the Collateral Inhibition
1. THE E F F E ~ V E
DURATION OF INHIBITION
Both the chemically transmitted collateral inhibition of the Mauthner
cell in the brain and the crossed inhibition in the spinal cord last a few
tens of milliseconds. Although we have not investigated the duration
of the mechanical muscle response in the Mauthner reflex, it is probably
declining by the time these inhibitions have ended (cf. Auerbach and
Bennett, 1969a,b). The electrical inhibition acts very quickly (Fig. 37B ),
and the total effect of the collateral inhibitions in the brain is enormously
to reduce the chances of either Mauthner cell firing a second time
while the reflex response is rising or is near its peak. It seems reasonable that the powerful tail flip should neither be reactivated while at
its peak nor opposed by an oppositely directed one at this same time.
The former possibility is disallowed by the phenomenon of fatigue,
the latter by the crossed inhibition in the cord. The cranial movements
J. DIAMOND
welcome attention of birds like the herons and bitterns, which catch
fish from a wading position.
The fact that birds which prey on fish do so successfully, and improve their performance as they grow to maturity, does not invalidate
the probable importance of the startle-response as an avoidance reaction
particularly developed to help shallow-living fish escape such birds.
It is significant that the “Mauthnerian apparatus” is absent or poorly
developed in tailIess fish, in almost all species living mostly at the
bottom, and in those showing eellike (anguilliform) movements; it is
interesting too that Mauthner cells are absent in anuran tadpoles with
small tails and most prominent in those with large ones, while on
metamorphosis of these species into tailless adult forms the Mauthner
cells atrophy altogether ( Stefanelli, 1951). The association of the Mauthner cell with the tail however has tended in the past to strengthen a
belief that the role of the cell is in swimming. We have rejected this
view in the preceding pages. The important points are the biological
environment of the tailed animals which have Mauthner cells, and
the characteristics of the circuitry of which the Mauthner neurons are
a part. Aquatic predators as well as birds may to some extent be put at
a disadvantage by the existence of the startle-response. However, it
may be that in this instance the lateral line system may be more important, and only in some species do fibers of the (anterior) lateral line
nerve extend to the Mauthner cells [Aronson (1963)-see also the
other origins of inputs to the Mauthner cell (Fig. 4)].
D. The Functions of the Collateral Inhibition
1. THE E F F E ~ V E
DURATION OF INHIBITION
Both the chemically transmitted collateral inhibition of the Mauthner
cell in the brain and the crossed inhibition in the spinal cord last a few
tens of milliseconds. Although we have not investigated the duration
of the mechanical muscle response in the Mauthner reflex, it is probably
declining by the time these inhibitions have ended (cf. Auerbach and
Bennett, 1969a,b). The electrical inhibition acts very quickly (Fig. 37B ),
and the total effect of the collateral inhibitions in the brain is enormously
to reduce the chances of either Mauthner cell firing a second time
while the reflex response is rising or is near its peak. It seems reasonable that the powerful tail flip should neither be reactivated while at
its peak nor opposed by an oppositely directed one at this same time.
The former possibility is disallowed by the phenomenon of fatigue,
the latter by the crossed inhibition in the cord. The cranial movements