PHYLUM ANNULATA 



493 



B 



An ci- 



Prc. cfin. 

 -An.ci 



4U9. 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. blastoccele ; Br. apical plate ; Ent. enteron ; J/s</. mesoderm ; 

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

 Prc. dm. proctodseura : Pt. or. ci. post-oral cilia ; St. dm. stomodoeum ; V. Nv. Cd. ventral 

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



Pf.a/n.ci" 



An.ci 



FIG 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 ; ZM /;", three stages in 

 the development of the'somatic mesoderm ; Cv.l. ccelome ; Ccul.'Epthm. coelomic epithelium ; 

 l)er Epthm deric epithelium ; M. vl. muscle-plate ; Msd. (som), somatic mesoderm ; 

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

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



