Route of Passive Ion Permeation in Epithelia

“Tight junctions” between cells in some epithelia actually provide the main route of passive ion permeation. The degree of junctional tightness may underlie important functional differences between different epithelia.     

The consumption of eggs of the perch, Perca fluviatilis L., by macroinvertebrates in the field

SUMMARY. 1. Perch egg masses, in a late stage of development, were collected from a small stillwater and the composition of the egg masses and the number of invertebrates which colonized them was recorded.
2. All of the invertebrates that colonized the egg masses were tested serologically for the presence of perch eggs and the ability of some invertebrates to eat live and dead perch eggs in the laboratory was determined.
3. Of the nineteen taxa that colonized the egg masses, only two species of flatworm and three species of caddisfly larva ate perch eggs in the field and, of these, only one genus of caddisfly larva ate live eggs in the laboratory.
4. It is concluded that the invertebrates present were not important predators of perch eggs.     

CONTEXT EFFECTS AND REFERENCE STANDARDS WITH MAGNITUDE ESTIMATION AND THE LABELED MAGNITUDE SCALE

Contextual shifts were observed for sweetness of a fruit beverage and for estimated tactile roughness of sandpapers. Midrange stimuli were judged to be less intense in the context of stronger items and more intense in the context of weaker items, a contrast effect. The use of a reference standard decreased the size of the contrast shift for the labeled magnitude scale but not for magnitude estimation.