THE COLLAR-CELLS IN HETEROCGLA. 45 
chloroform. The outlines of cells in the adjoining chamber are shown; the 
dark spot and the black dots are carmine, with which the sponge had been fed 
for four hours and a quarter. The preparation is unstained ; the light shading 
of the spherules is due to osmic acid. 
Fie. 22.—Living flagellate chamber from Acanthella stipitata, Carter, 
drawn to the same scale as figs. 1, 2, 11 c, 12, &c. The shaded dots are the 
bases of collar-cells, the white space the apopyle. 
