The Development of Phascolosonia. 155 



Wilson, E. B. , 1890, Origin of the mesoblast-bands in Annelids, in: 



J. Morph., Vol. 4. 

 —, 1892, The cell lineage of Nereis, ibid.. Vol. 6, No. 3. 

 — , 1895, Atlas of fertilization and karyokinesis, New York. 

 — , 1898, Cell lineage and ancestral reminiscence, in: Ann. New York 



Acad. Sc, Vol. 11. 

 V. "WiSTlNGHAUSEN , C. , 1891, Untersuchungen über die Entwicklung 



von Nereis Dumerilii, Th. 1, in: Mitth. zool. Stat. Neapel, Vol. 10. 



Explanatiou of Plates. 



All figures were drawn with the aid of the Abbe camera lucida. 



Abbreviations. 

 an anus 



cist $ astrosphere of the sperm nucleus 

 ast Ç astrosphere of the egg nucleus 

 hVpo blastopore 

 cd. d dorsal cord of ectoderm 

 el. fill yellow chlorogogue cells 

 cl. rpr reproductive cells 

 coel coelom 



can't, cre'oe circumoesophageal connective 

 cp^cl. coel coelomic corpuscle 



crc. ji'or postoral circlet of cilia, or cells bearing these cilia 

 Cfc. pr'or preoral circlet of cilia 

 eta cuticula 



e small cells probably derived from a telomesoblast 

 ec'drni ectoderm 

 en'drm endoderm 



en\lrm. d large median-dorsal endoderm cell 

 gn supraoesophageal ganglion 

 ms'drm coelom esoblast 

 mil. crc circular muscle fibres 

 mu. oe muscle fibres attached to the oesophagus 

 mu. ret muscle fibres attached to the rectum 

 mu. rtr. ac accessory retractor muscles 

 mil. rtr. d dorsal retractor muscle 

 m,u. rtr v ventral retractor muscle 

 rCmu. a. v antero-ventral neuromuscular organ 

 n^mu. d. I dorso-lateral neuromuscular organ 



