PHYLUM ANN PLATA 



505 



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

 like seta.' on each segment, and it has only a single pair of nephridia, which are 



Fio. 402.— Trochophore of Folygordius neapolitanus. A, lateral view of entire larva ; 

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

 An. ci. anal cilia ; Bl. blastociele ; Br. apical plate ; Ent. enteron ; Msd. mesoderm ; Msd. 

 M. mesodermal bands ; Xph. head-kidney ; Oc. eye-spot ; Pr. or. ri. cilia of prototroch ; Pre. 

 dm. proctodeum ; 1't. or. ci. post-oral cilia : St. dm. stomodaeum ; V. Nv.C'd. ventral nerve-cord. 

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



tUBt 



Msd .'/it ) 



Pre. dm. 



Pr.an.ci. 



An.ci 



~An ci. 



Fio. 403.— Later stage in the development of Folygordius neapolitanus, in which the 

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

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

 development of the somatic mesoderm : Co?l. ctelome : ail. Bpthm. ceelotaic epithelium ; her. 

 Ejithm. deric epithelium; M.pl. muscle-plate: Mid. (mh.), somatic mesoderm; Msd. (spl), 

 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 3ingle (longitudinal) layer of 

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



