4. ANALYSIS OF FACTORS INVOLVED IN~SYMBIOSIS
31
The observations were conducted in Pyrex Petri dishes containing
50 ml of water or in finger bowls with 100 ml of water and observed
under a stereomicroscope appropriately illuminated so that the diffuse
light did not influence the miracidia. A known number of miracidia
was added to each dish or bowl and a pyramid containing the test
chemical, or a control pyramid, was placed in the center of the container. In addition, Australorbis gbbratus tissues were also used in
another series of observations. Uninterrupted observations were
recorded for 10-15 min during the experiments.
FIQ. 6. Responses of Schistosoma rnansoni miracidia to test pyramids (contact without
return). A, Normal change of direction upon contact with an obstruction; B,
increased random turning ; C, directed turn at a distance ; D, encircling at a distance ;
E, 180" turnback; F, circus movements. (After MacInnis, 1966.)
Schistosorna rnansoni rniracidia normally swim with a uniform
speed in a straight line while rotating clockwise or counterclockwise
along the longitudinal axis. If such a miracidium should encounter a
surface, including the surface film, it changes its direction of movement
so as to by-pass the obstruction and continues to swim normally
(Fig. 5A). MacInnis reported that if miracidia enter the vicinity
(0-5 mm) of a snail or impregnated pyramid, they portray a variety
of behavior patterns. These can be summarized as follows. (1) They
sometimes increase their speed of swimming. This, according to the
definition of Fraenkel and Gunn (1961), is known as " chemo-orthokinesis" (i.e. increased linear velocity in response to a chemical
31
The observations were conducted in Pyrex Petri dishes containing
50 ml of water or in finger bowls with 100 ml of water and observed
under a stereomicroscope appropriately illuminated so that the diffuse
light did not influence the miracidia. A known number of miracidia
was added to each dish or bowl and a pyramid containing the test
chemical, or a control pyramid, was placed in the center of the container. In addition, Australorbis gbbratus tissues were also used in
another series of observations. Uninterrupted observations were
recorded for 10-15 min during the experiments.
FIQ. 6. Responses of Schistosoma rnansoni miracidia to test pyramids (contact without
return). A, Normal change of direction upon contact with an obstruction; B,
increased random turning ; C, directed turn at a distance ; D, encircling at a distance ;
E, 180" turnback; F, circus movements. (After MacInnis, 1966.)
Schistosorna rnansoni rniracidia normally swim with a uniform
speed in a straight line while rotating clockwise or counterclockwise
along the longitudinal axis. If such a miracidium should encounter a
surface, including the surface film, it changes its direction of movement
so as to by-pass the obstruction and continues to swim normally
(Fig. 5A). MacInnis reported that if miracidia enter the vicinity
(0-5 mm) of a snail or impregnated pyramid, they portray a variety
of behavior patterns. These can be summarized as follows. (1) They
sometimes increase their speed of swimming. This, according to the
definition of Fraenkel and Gunn (1961), is known as " chemo-orthokinesis" (i.e. increased linear velocity in response to a chemical