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 

 external 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. 5. 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 lacunse 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, a, portion of one of the spiral canals ; b, b, portion of the succeeding whorl of 

 the same canal ; c, c, meridional canals of the inner whorl ; </, 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 cour? e 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 1 , a 2 , through the cavity of the chambers, whilst in the 

 alternate whorls b, b 1 , b', 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 d 2 , 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, b' b', transverse sections of the two spiral canals ; c, c 1 , c 2 , 

 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, 



4n2 



