PHYLUM ANNULATA 



493 



B 



An ci 



FIG. 409. Trochophore of Polygordius neapolitanus. A, lateral view of entire larva ; 

 B, diagrammatic vertical section ; C, transverse section through the plane ab in B ; An. 

 anus ; An. ci. anal cilia ; Bl. blastocoele ; Br. apical plate ; Ent. enteron ; M sd. mesoderm ; 

 Msd. bd. mesodermal bands ; Nph. head-kidney ; Oc. eye-spot ; Pr. or. ci. cilia of prototroch ; 

 Prc. dm. proctodseura ; Pt. or. ci. post-oral cilia ; St. dm. stomodseum ; F. Nv. Cd. ventral 

 nerve-cord. (From Parker's Biology, partly after Fraipont.) 



FiO. 410. Later stage in the development of Polygordius neapolitanus, in which the 

 posterior part of the trochophore has become elongated and segmented ; A, entire larva ; 

 B, vertical section ; C, transverse section along the plane ab in B ; Z)i I)'--, three stages in 

 the development of the'somatic mesoderm; C<xl. coelome ; Ccel.'Epthm. coelomic epithelium; 

 Der. Epthm deric epithelium ; M. pi. muscle-plate ; Msd. (som), somatic mesoderm ; 

 M sd. (spl), splanchnic mesoderm ; o. eye ; t. tentacle. Other letters as in preceding 

 figure. (From Parker's Biology, partly after Fraipont.) 



