EXPLANATION OF THE PLATES. 
587 
of which passes between each chamber and the one that succeeds, opening at 
each end into the spiral canal ; c, the straight canals which come off from the 
spiral canals into the solid umbilical deposit, and pass through it direct to the 
extemal surface ; d, the converging canals, which pass inwards from the meri- 
dional canals in the intraseptal spaces ; e, the surface of the innermost whorl 
displayed by this section, on which are seen the meridional canals giving off 
their diverging branches in pairs. Magnified 30 diameters. 
Fig. 3. Central portion of a section passing through the median plane of a specimen 
remarkable for the very small size of the primordial segment. Magnified 60 
diameters. 
Fig. 4. Central portion of a section (viewed under the same magnifying power as the 
preceding) passing through the median plane of a specimen remarkable for 
the very large size of its primordial segment. Magnified 60 diameters. 
Fig. 6. Central portion of a section parallel to the median plane, but a little above it, 
showing one of the spiral canals and the central system of lacunae in which it 
originates. Magnified 60 diameters. 
Fig. 6. Portion of a section taken in a direction parallel to the median plane but much 
nearer the surface, showing parts of the canal-system of the outer whorls: 
«, a, portion of one of the spiral canals ; h, h, portion of the succeeding whorl of 
the same canal ; c, c, meridional canals of the inner whorl ; c', c', origins of the 
meridional canals of the outer whorl, with their first pairs of diverging 
branches ; d, d, origins of the canals that penetrate the solid umbilical deposit, 
which soon change their course and become vertical ; e, transverse sections of 
vertical canals. Magnified 80 diameters. 
Fig. 7. Marginal portion of a section taken in the same direction as fig. 2, and passing, 
in the whorls a, a\ a^, through the cavity of the chambers, whilst in the 
alternate whorls b, b\ If, it passes along the septal plane ; at c, c, are seen the 
meridional canals transversely divided near the points at which they give off 
their diverging branches. Magnified 60 diameters. 
Fig. 8. Portion of a section taken through the median plane, showing the alternate 
position of the chambers b, b, b, with reference to those a, a, a, of the interior 
whorl, and those c, c, c, of the exterior whorl ; at d, d\ and are seen the 
external orifices of the diverging branches of the canal-system ; and at e, e[ are 
seen the junctions at their orifices of the adjacent branches of two distinct 
pairs, such junctions being generally connected with the septal apertures 
occupied by stolons of sarcode. Magnified 60 diameters. 
Fig. 9. Section of Polystomella crispa, taken through the umbilical axis: a, a', solid 
umbilical deposit ; b b, V V , transverse sections of the two spiral canals ; c, &, 
portions of the meridional canals ; d, csecal diverticula for the ‘ retral pro- 
cesses e, septal apertures. Magnified 50 diameters. 
Fig. 10. Portion of a section of Polystomella crispa taken through the median plane, 
4 H 2 
