. Elementary text-book of zoology. Zoology. 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 Annel
. Elementary text-book of zoology. Zoology. 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. 3 Ser., Tom VII. Lacaze-Duthiers, " Recherches sur le Bonellia," Ann. ili-x ,SV>. -\« 1858. W. Keferstein. " Beitriige zur anatomischen und systematischen Keimtniss der Sipunculiden,"
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