339 



a sexually mature Cestoid still fixed by an appendage bearing the embryonic 

 hooks. Archigvtes Sieboldii Lkt. With two weak suckers and a caudal 

 appendage. 



Order 4. NEMERTINI* = RH YNCHOC<ELA. 



Elongated, frequently band-skewed Platyhelminthes, with straight 

 alimentary canal opening by an anus, and with 

 a separate protrusiUe proboscis. Usually with 

 two ciliated pits in the, cephalic region. The 

 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- 



FiG. 276. Tetrastemma 

 obscurum (after M. 

 Schultze). Young 

 specimen about 3 lines 

 in length; O, mouth; 

 D, intestine ; A, anus ; 

 Bg, blood vessels; R, 

 proboscis armed with 

 stylet ; Ex, lateral 

 trunks of the excre- 

 tory system; P, ex- 

 cretory pore; G, 

 ciliated pit ; Nc, nerve 

 centre ; Ss, lateral 

 nerve trunks ; Oc, 



* A. de Quatrefages, " Memoire sur la famille des 

 Nemertines," Ann. des Sc. Nat.. Ser. 3, Tom. VI., 1846. 

 Mclntosh, " On the Structure of the British Nemerte- 

 ans," Transact. Edirib. Royal Soc., Tom XXV., 1 & 2. 



Barrois, " Memoire sur 1'Embryplogie des N6mertes," Paris, 1877. Hubrecht, 

 " Untersuchungen iiber Nemertinen, etc.," Niederl. Arckiv.. Tom. II. 



