4. ANALYSIS O F FACTORS INVOLVED I N SYMBIOSIS
83
behavior of the larvae of Stephanostomum tenue. Earlier, Cheng (1962,
1963c) had shown that in the case of Helisoma trivolvis infected with
another trematode, Echinoparyphium sp., no dramatic reduction of
glycogen occurs in the host’s intact hepatopancreatic cells. Echinoparyphium sp., like Stephanostomum tenue, includes redial rather than
sporocyst generations in its life cycle. Since rediae possess a functional
mouth, it has been shown that the intramolluscan rediae acquire their
carbohydrate requirements by ingesting glycogen-containing cells
primarily, leaving the intact cells essentially unaltered as far as their
glycogen content is concerned. Thus in the case of 8. tenue, the rediae
presumably also ingest cells directly without the necessity of converting
the host’s stored glycogen t o glucose, hence one can expect the levels of
reducing sugars to remain at a comparable level in infected and
uninfected Nassarius obsoletus. It should be noted that rediae do not
acquire their nutrient requirement exclusively by ingestion. The
electron microscope studies by G. Rees (1966), Bils and Martin (1966),
Krupa et aE. (1966) and Cheng and Hamamoto (unpublished) have
revealed the occurrence of microvilli on redial surfaces which suggests
that rediae may also absorb certain nutrients.
In sporocyst-containing hosts, it still remains uncertain what causes
the breakdown of stored glycogen to glucose. Preliminary experiments
reported by Clieng (1963d) indicate that the hydrolyzing enzyme is not
of parasite origin , which appears reasonable since evidences on membrane
permeability have indicated fairly conclusively that large protein
molecules, such as a carbohydrase, could not permeate the cell membrane of the host’s hepatopancreatic cells. It is thus necessary to
speculate that the presence of sporocysts in some way triggers the host’s
native enzymes to increase the rate of glycogen degradation.
As stated, it is known that glucose will pass through both the
sporocyst wall and the body surface of developing cercariae ; however,
no direct evidence is yet available which indicates whether the glucose
enters by simple diffusion or by some other mechanism. The finding by
Cheng and Snyder (196213) and Cheng (1964a) that there is alkaline
phosphatase activity associated with the body surface of cercariae may
be suggestive that glucose, or perhaps some other substance, is conducted across the body wall by phosphorylative transport. This
mechanism has been considered to be possible by Danielli (1952).
Certainly the presence of microvilli on the surface of sporocysts, as
demonstrated by the electron microscope studies of Bils and Martin
(1966), suggests that the sporocyst wall is an absorptive surface.
Similarly James et al. (1966), who have also studied the fine structure
of the sporocyst wall, have suggested that it is absorptive.
83
behavior of the larvae of Stephanostomum tenue. Earlier, Cheng (1962,
1963c) had shown that in the case of Helisoma trivolvis infected with
another trematode, Echinoparyphium sp., no dramatic reduction of
glycogen occurs in the host’s intact hepatopancreatic cells. Echinoparyphium sp., like Stephanostomum tenue, includes redial rather than
sporocyst generations in its life cycle. Since rediae possess a functional
mouth, it has been shown that the intramolluscan rediae acquire their
carbohydrate requirements by ingesting glycogen-containing cells
primarily, leaving the intact cells essentially unaltered as far as their
glycogen content is concerned. Thus in the case of 8. tenue, the rediae
presumably also ingest cells directly without the necessity of converting
the host’s stored glycogen t o glucose, hence one can expect the levels of
reducing sugars to remain at a comparable level in infected and
uninfected Nassarius obsoletus. It should be noted that rediae do not
acquire their nutrient requirement exclusively by ingestion. The
electron microscope studies by G. Rees (1966), Bils and Martin (1966),
Krupa et aE. (1966) and Cheng and Hamamoto (unpublished) have
revealed the occurrence of microvilli on redial surfaces which suggests
that rediae may also absorb certain nutrients.
In sporocyst-containing hosts, it still remains uncertain what causes
the breakdown of stored glycogen to glucose. Preliminary experiments
reported by Clieng (1963d) indicate that the hydrolyzing enzyme is not
of parasite origin , which appears reasonable since evidences on membrane
permeability have indicated fairly conclusively that large protein
molecules, such as a carbohydrase, could not permeate the cell membrane of the host’s hepatopancreatic cells. It is thus necessary to
speculate that the presence of sporocysts in some way triggers the host’s
native enzymes to increase the rate of glycogen degradation.
As stated, it is known that glucose will pass through both the
sporocyst wall and the body surface of developing cercariae ; however,
no direct evidence is yet available which indicates whether the glucose
enters by simple diffusion or by some other mechanism. The finding by
Cheng and Snyder (196213) and Cheng (1964a) that there is alkaline
phosphatase activity associated with the body surface of cercariae may
be suggestive that glucose, or perhaps some other substance, is conducted across the body wall by phosphorylative transport. This
mechanism has been considered to be possible by Danielli (1952).
Certainly the presence of microvilli on the surface of sporocysts, as
demonstrated by the electron microscope studies of Bils and Martin
(1966), suggests that the sporocyst wall is an absorptive surface.
Similarly James et al. (1966), who have also studied the fine structure
of the sporocyst wall, have suggested that it is absorptive.