. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. NEMERTINI. 339 Nc a sexually mature Cestoid still fixed by an appendage bearing the embryonic hooks. Archiffctcs Sieboldii Lkt. With two weak suckers and a caudal appendage. Order 4.—NEMERTINI*=RHYNCIIOCCELA. Elongated, frequently band-shaped Platyhelininthes, with straight alimentary canal opening by an anus, and ivith a separate protrusible proboscis. Usually ivith tiuo ciliated pits in the cephalic region. TJie sexes are separate. The Nemertines are distinguished not only by their elonga
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. NEMERTINI. 339 Nc a sexually mature Cestoid still fixed by an appendage bearing the embryonic hooks. Archiffctcs Sieboldii Lkt. With two weak suckers and a caudal appendage. Order 4.—NEMERTINI*=RHYNCIIOCCELA. Elongated, frequently band-shaped Platyhelininthes, with straight alimentary canal opening by an anus, and ivith a separate protrusible proboscis. Usually ivith tiuo ciliated pits in the cephalic region. TJie sexes are separate. The Nemertines are distinguished not only by their elongated form, but also by their con- siderable size and high organization. Thick layers of muscles, traversed by connective tissue, are spread beneath the integument, which con- tains pigment as well as flask-shaped mucous glands. The external layer of longitudinal muscles, strongly developed in the Anopla, is wanting in the Enopla (Nemertines, the probos- cis of which is armed with stylets), in which group there is only an outer layer of circular muscles and an inner layer of longitudinal muscles. A long tubular protrusible proboscis, which is sometimes armed with stylet-shaped rods, is always found at the anterior end of the body above the buccal cavity, and projects through a special prseoral opening (fig. 276), and can be retracted into a special muscular sheath separate from the body cavity. At the bottom of the principal portion of the proboscis, there is in many Nemertines (Enopla) a large spine, which is directed forwards, and at its sides numerous small secondary spines in pouches. The posterior glandular portion of the proboscis, to which retractor muscles are attached, is, according to Claparede, to be regarded as a poison apparatus. When the proboscis is pro- * A. do Quatrefages, " Memoire sur la famille des Nemertines," Ann. des So. Ser. 3, Tom. VI., 184G. Mclntosh, " On the Structure of the British Nemerte- ans," Transact. Edlnb. Royal Soc.
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