32
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
stimulus). (2) Other miracidia, when in the same situation, turn
abruptly back and forth in a " wigwag " manner (Fig. 5B). This
movement appears to be an exaggeration of the rotation of the miracidium along its longitudinal axis and subscribes to the definition of
" chemo-klino-kinesis " of Fraenkel and Gunn (i.e. change in the rate
of random turning or angular velocity in response to a chemical
stimulus). According to MacInnis, this type of movement, which may
commence at 7 mm or more from the pyramid, appears to aid in locating
a gradient of diffusing chemicals, and thus the source. (3) A third type
of behavior involves miracidia not swimming directly towards the test
object. I n these instances, if a miracidium is attracted by the pyramid
it suddenly turns and swims toward test object (Fig. 5C). This response
can be considered as Fraenkel and Gunn's " chemo-tropo-taxis " in
part (i.e. locomotion straight towards or away from the source of the
chemical stimulus ; the result of simultaneous comparison by two
receptors). MacInnis has reported, however, that the directional turn
is often accompanied by increased speed (chemo-ortho-kinesis) and
increased " wigwagging " (chemo-klino-kinesis). The combination of
these three behavior patterns had been reported by Campbell and Todd
(1955a) who referred to the condition as " excitement ". (4) A fourth
type of reactional behavior involves a complete or incomplete circling
3-5mm away from the test object (Fig. 5D). This behavior pattern
can be considered as " chemo-klino-taxis " (i.e. movement directly
to the stimulus, or locomotion along the line to the stimulus, modified
by regular symmetrical deviations ; only one receptor is needed).
MacInnis has suggested that this behavior might be explained as a
reaction occurring at a boundary of the moving front of the diffusing
chemical, or at one place in the gradient where the concentration of the
chemical is at the threshold of intensity for a positive reaction.
( 5 ) A fifth type of behavior is displayed by miracidia moving away
from the source of the chemical stimulant. These execute a 180" turn,
thus pointing themselves toward the source of the stimulus (Fig. 5E).
This type of behavior is considered by Fraenkel and Gunn (1961) as
" chemo-tropo-taxis ".
(6) The last type of behavior occurs in the zone of a diffusing chemical
where some miracidia change from the normal swimming behavior to
swimming in a small circle (Fig. 5F). This type of behavior appears to
be identical with the " whirling dance " of Davenport et al. (1962). It
has also been described by Campbell (1961) for the miracidium of
Fascioloides magna, and according to Campbell was found by Hugghins
for the miracidium of Hysteromorpha triloba, a strigeid trematode.
Earlier, Fraenkel and Gunn (1961) had reported this behavior among
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
stimulus). (2) Other miracidia, when in the same situation, turn
abruptly back and forth in a " wigwag " manner (Fig. 5B). This
movement appears to be an exaggeration of the rotation of the miracidium along its longitudinal axis and subscribes to the definition of
" chemo-klino-kinesis " of Fraenkel and Gunn (i.e. change in the rate
of random turning or angular velocity in response to a chemical
stimulus). According to MacInnis, this type of movement, which may
commence at 7 mm or more from the pyramid, appears to aid in locating
a gradient of diffusing chemicals, and thus the source. (3) A third type
of behavior involves miracidia not swimming directly towards the test
object. I n these instances, if a miracidium is attracted by the pyramid
it suddenly turns and swims toward test object (Fig. 5C). This response
can be considered as Fraenkel and Gunn's " chemo-tropo-taxis " in
part (i.e. locomotion straight towards or away from the source of the
chemical stimulus ; the result of simultaneous comparison by two
receptors). MacInnis has reported, however, that the directional turn
is often accompanied by increased speed (chemo-ortho-kinesis) and
increased " wigwagging " (chemo-klino-kinesis). The combination of
these three behavior patterns had been reported by Campbell and Todd
(1955a) who referred to the condition as " excitement ". (4) A fourth
type of reactional behavior involves a complete or incomplete circling
3-5mm away from the test object (Fig. 5D). This behavior pattern
can be considered as " chemo-klino-taxis " (i.e. movement directly
to the stimulus, or locomotion along the line to the stimulus, modified
by regular symmetrical deviations ; only one receptor is needed).
MacInnis has suggested that this behavior might be explained as a
reaction occurring at a boundary of the moving front of the diffusing
chemical, or at one place in the gradient where the concentration of the
chemical is at the threshold of intensity for a positive reaction.
( 5 ) A fifth type of behavior is displayed by miracidia moving away
from the source of the chemical stimulant. These execute a 180" turn,
thus pointing themselves toward the source of the stimulus (Fig. 5E).
This type of behavior is considered by Fraenkel and Gunn (1961) as
" chemo-tropo-taxis ".
(6) The last type of behavior occurs in the zone of a diffusing chemical
where some miracidia change from the normal swimming behavior to
swimming in a small circle (Fig. 5F). This type of behavior appears to
be identical with the " whirling dance " of Davenport et al. (1962). It
has also been described by Campbell (1961) for the miracidium of
Fascioloides magna, and according to Campbell was found by Hugghins
for the miracidium of Hysteromorpha triloba, a strigeid trematode.
Earlier, Fraenkel and Gunn (1961) had reported this behavior among