PHYLUM ANNUL ATA 



505 



system and in the presence of ciliated pits ; but it has a row of comb- 

 like sjta? on each segment, and it has only a single pair of nephridia, which are 



Br 



B 



An ei 



r. 



Fi;. 40-2. Trochophore of Polygordius neapolitanus. A, lateral view of entire larva ; 

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

 An. ci. anal cilia; El. blastocoele ; Br. apical plate; Ent. enteron ; Msd. niesoderm ; Msd. 

 li<1. mesoderrnal bands ; Sph. head-kidney ; Oc. eye spot ; Pr. or. ci. cilia of prototroch ; Prc. 

 <!>. proctodajum ;Pt. or. ci. post-oral cilia : St. <i,n. stomodajum ; V. Nv.Cd. ventml nerve-cord. 

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



r.or.ci 



FIG. 403. Later stage in the development of Polygordius neapolitanus, in which the 

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

 B, vertical section ; C, transverse section along the plane ab in B ; -D 1 D 3 , three stages in the 

 development of the somatic mesoderm : Ccel. coelome : cctl. Epthm. coaloiuic epithelium ; Der. 

 Ef.tlim. deric epithelium; M.pl. mnscle-plate : Msd. (som.), somatic mesoderm; Msd. (*pl), 

 splanchnic mesoderm ; 0. eye ; t. tentacle. Other letters as in preceding figure. (From 

 Parker's Biology, partly after Fraipont.) 



situated in the peristomium. There is only a single (longitudinal) layer of 

 muscles in the body-wall ; the reproductive apparatus is not known. 



