386 



ANNELIDA. 



sc 



fused with the mouth segment. J\'ttig (Sti/larnt} proboxcidea 0. Fr. Mull. 

 N. jMtrax/'fa Schm. Both species have filiform pnestomium. Cha-toi/nsti-i- 

 rermlcularisQ. Fr. Miill. 



Sub-class 2. GEPHYKEA.* 



Worms with cylindrical body, without external segmentation, with 

 terminal or ventral mouth ; with cerebral ganglion, cesophayeal ring 

 and ventral cord. Settv are sometimes present. 



The Gephyrea possess an elongated cylindrical body and live, as do 

 the Holothuria, in sand and ooze in the sea. The characters which 

 distinguish them as Annelids are the possession of an oesophageal 

 ring connected with a cerebral ganglion and of a ventral cord par- 

 tially surrounded by ganglion 

 cells. The larva? of the Chce- 

 tifera present traces of seg- 

 mentation (see below, p. 391), 

 while in the Achceta the body 

 cavity remains simple. Of sense 

 organs, eye spots have been 

 observed ; these in certain 

 SipuncuUdce lie directly upon 

 the brain ; there are also dermal 

 papillse, into which nerves 

 enter. 



The structure of the integu- 

 ment is similar to that of the 

 Annelida; the thick upper 

 cuticular layer rests upon a 

 cellular matrix, and is not un- 



Fie. 3ii. Young Ediiurus from the iiventrai frequently wrinkled. There is 

 side (after Hatschek). 0. Month at the base i , mi 



of the proboscis; SO, sopha*eal commis- n external segmentation. The 



sure ; BS, ventral cord ; A, anus ; if, hooks, connective tissue dermis is of 



considerable thickness and en- 

 closes numerous glandular tubes, which open to the exterior by pores 

 in the epidermis. Below this is the strongly developed dermal muscular 

 tunic, which is regularly composed of an outer layer of circular fibres 



* Quatrefages," Memoire sur 1'Echiure," Ann. (h-s Sc. Xnt.. 3 Ser., Tom VII. 

 Lacaze-Duthiers, " Recherches sur le Bonellia," Ann. ili-x ,SV>. -\t.. 1858. 

 W. Keferstein. " Beitriige zur anatomischen und systematischen Keimtniss der 

 Sipunculiden," Zcitscltr fur n'/M. Zoologic, Tom XV., 18(io. B. Hatschek. 

 " Ueber Entwickelung?geschichte des Echiurus," etc. Wien, 1880. J. W. 

 Spengel, "Beitrage zur Kenntniss der Gephyreen. I. Mitthi-H. mix dcr zvolo- 

 gischen xtutiun :tt JVeajwl, 1879 ; II. Zcitschr.fur n-ias. Ztwl., Tom XIV., 1881. 



