Introduction to Animal Morphology. 141 



or one of the ambulacra! areas (s. internee) ; or may surround 

 the body equatorially (s. marginales) ; or may divide the 

 sides uniting with the marginal semitee (s. laterales) ; or may 

 lie in front of, or around, the anus (s. sub-anales). Around 

 the mouth is a bueeal membrane bearing pcdicellarice (modi- 

 tchcl), usually with three valves, and having a 

 calcareous, netted axis in a soft, mucous tissue, and with 

 simple muscle bundles uniting the branches. These may 

 hr : i. P. glnhiferce with a solid stiff axis and a globular 

 'ike a closed three-leafed bud. 2. P. stereophyllce 

 with a hollow axis and a round, calcareous head. 3. P. tri- 

 dentes shorter, with a hollow axis, and serrated arms with 

 incurved points. 4. P. ophiocephalae with a longer pillar, 

 and leaf-like limbs. 



The ambulacral system consists of a circum-oral 

 ring, five pedunculated Polian vesicles, cavernous in 

 structure, with netted, unstriped fibres in the wall on 

 th<> membrane over the dental apparatus, and five 

 ambulacral canals, one between each row of holes, 

 while proximal processes pass from the ambulacral 

 canals to the buccal tentacles (J \-rn\-r}. The tube- 

 feet maybe alike (ambulacra homceopoda), or dissimilar 

 (a. heteropoda), and each has at its free end a radially 

 plaited sucking- membrane, under which is a cal- 

 careous, netted rosette, and sometimes a still deeper, 

 calcareous ring. Arcuated and branched spicules 

 often abound in the wall of thepedicelli. 1 leteropodal 

 forms like Spatantfus may have (a) simple fed, with 

 -inking spiruliovrnus fort, with an 

 entire or digital*- margin ; (y) sensitive fret with broad 

 pencil-like ends and flattened knobs, supported on 

 line, rod-like styles ; r tfill-fe.-t with pinnated margin ; 

 biiM-al petlio-lli with no rinLT, and a rudimental 

 rosette. Tb- from the, madreporiform 



its walls stiff with spicules, but 



