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Harald Tichy and Ewald Gingl
than the examined spider (Barth et al. 1988) does, however. Here a smaller pore
with tighter "plugging" might be advantageous. Further, if a drier environment
were to demand a reservoir of lymph larger than that of the spider in order to
maintain a slight flow with a constant electrolyte concentration in the background,
the large outer lymph cavity of insects might serve as a source. In this case both
the cuticle just outside the outer lymph cavity and the dendritic sheath would be
needed as water barriers.
ambient
humidity
mode of
action
important
parameter
Mechanrcal hygrometer
swelling shrinking
of hygroscopic structures
relative humidity
Psychrometer
small great
temperature depression
vapor pressure
Electrochemical hygrometer
small great
change in concentration
saturation deficit
Fig. 5. Models for hygroreception. In mechanical hygrometers activity is initiated by swelling or shrinking of hygroscopic sensillum structures, in psychrometers the degree of cooling due to evaporation is used to measure humidity, and in electrochemical hygrometers
humidity affects electrolyte concentration just outside the dendrites. In the mechanical hygrometer model, movement of water is from the air into the sensillum and from the sensillum into the air, and in both the psychrometer and the electrochemical model it is from the
sensillum towards the outside. Mechanical hygrometers would response to the relative humidity, psychrometers to the partial pressure of water vapor and electrochemical hygrometers to the saturation deficit of the air.
These models are interesting not only in relation to structural features. They also
pose some intriguing questions as to the parameters governing the responses. If it
is assumed that the recorded responses of hygroreceptors are not affected by temperature per se, it follows that the different types of hygroreceptors would respond
to different parameters when tested with humidity stimuli at different temperatures. Hygroreceptors acting as mechanical hygrometers would produce the same
response to the same relative humidity, regardless of the ambient temperature.
Those acting as psychrometers would produce the same response to the same va-
Harald Tichy and Ewald Gingl
than the examined spider (Barth et al. 1988) does, however. Here a smaller pore
with tighter "plugging" might be advantageous. Further, if a drier environment
were to demand a reservoir of lymph larger than that of the spider in order to
maintain a slight flow with a constant electrolyte concentration in the background,
the large outer lymph cavity of insects might serve as a source. In this case both
the cuticle just outside the outer lymph cavity and the dendritic sheath would be
needed as water barriers.
ambient
humidity
mode of
action
important
parameter
Mechanrcal hygrometer
swelling shrinking
of hygroscopic structures
relative humidity
Psychrometer
small great
temperature depression
vapor pressure
Electrochemical hygrometer
small great
change in concentration
saturation deficit
Fig. 5. Models for hygroreception. In mechanical hygrometers activity is initiated by swelling or shrinking of hygroscopic sensillum structures, in psychrometers the degree of cooling due to evaporation is used to measure humidity, and in electrochemical hygrometers
humidity affects electrolyte concentration just outside the dendrites. In the mechanical hygrometer model, movement of water is from the air into the sensillum and from the sensillum into the air, and in both the psychrometer and the electrochemical model it is from the
sensillum towards the outside. Mechanical hygrometers would response to the relative humidity, psychrometers to the partial pressure of water vapor and electrochemical hygrometers to the saturation deficit of the air.
These models are interesting not only in relation to structural features. They also
pose some intriguing questions as to the parameters governing the responses. If it
is assumed that the recorded responses of hygroreceptors are not affected by temperature per se, it follows that the different types of hygroreceptors would respond
to different parameters when tested with humidity stimuli at different temperatures. Hygroreceptors acting as mechanical hygrometers would produce the same
response to the same relative humidity, regardless of the ambient temperature.
Those acting as psychrometers would produce the same response to the same va-