Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 AlfNELIDA. fused with the mouth segment. Nais (Stylaria) prohoscidea O. Fr. Miill. N. parasita Schm. Both species have a filiform piaestomium. Chatogaster vermicnlarig 0. Fr. Miill. Sub-class 2.âGephyrea.* Worms with cylindrical body, without external segmentation, with terminal or ventral mouth; ivith cerebral (jamjlion, oesoj)harjeal ring and ventral cord. Setae are sometimes present. The Gejyhyrea possess an elongated cylindrical bod
Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 AlfNELIDA. fused with the mouth segment. Nais (Stylaria) prohoscidea O. Fr. Miill. N. parasita Schm. Both species have a filiform piaestomium. Chatogaster vermicnlarig 0. Fr. Miill. Sub-class 2.âGephyrea.* Worms with cylindrical body, without external segmentation, with terminal or ventral mouth; ivith cerebral (jamjlion, oesoj)harjeal ring and ventral cord. Setae are sometimes present. The Gejyhyrea 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 larvae of the Ghce- ti/era present traces of seg- mentation (see below, p. 391), â while in the Achceta the body cavity remains simple. Of sense L * \ organs, eye spots have been '^ \ observed; these in certain Sipuncididce lie directly upon the brain; there are also dermal papillae, 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- FiG. 311.âYoung jScMurus from the ventral frequently wrinkled. There is side (after Hatschek). 0, Mouth at the base ^^ external segmentation. The of the proboscis; SC, CEsophageal commas. _ _ ^ Bure; £5, ventral cord; ^, anus; IT,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,' M^moire sur TEchiure,' Ann. dcs Sc. 3 Tom VII. Lacaze-Duthiers, ' Kecherches sur 1» Bonellia,' Ann. dcs Sc. Kat., 1858. W. Keferstein, '
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