NEMERTEA. 639 



sac, rarely more, containing two or three calcareous stylets pointed at one 

 end, at the other provided with a head like a nail's. Both central and 

 lateral stylets can be thrown off and formed anew. The muscular bulb 

 contains glands ; its reservoir is filled with liquid which is perhaps poisonous. 

 The non-eversible section of the proboscis has glandular walls and is filled 

 with liquid. The function of the organ is doubtful. It may be in part 

 tactile, in part offensive or defensive 1 . 



The mouth is ventral, in front of the ganglia in Hoplonemertea, behind 

 them in other Nemertea. It leads into a straight oesophagus with longi- 

 tudinal muscular fibres in its walls ; an intestine which, except in the adult 

 Carinella, Cephalothrix, and Carinoma, is provided with short lateral and 

 usually opposite caeca. The latter in Pelagonemertes number only thirteen 

 pairs, are long and branched at their ends. Both oesophagus and intestine 

 are ciliated and contain glands in their walls. The anus is terminal. There 

 is a system of coelomic blood spaces communicating anteriorly in the head 

 and posteriorly by a supra-anal commissure. The spaces in the head and 

 oesophageal region of Palaeo- and Schizo-nemertea are lacunar, i. e. large 

 and somewhat irregular in outline, whereas posteriorly they become vessels, 

 i. e. smaller and either circular or oval in section, as they are throughout 

 the whole system in Hoplonemertea. They are lined throughout by an 

 epithelium, and the vessels generally possess a muscular wall of circular 

 and sometimes also longitudinal fibres. There are two principal longi- 

 tudinal and lateral spaces in Carinella, Cephalothrix, and Carinoma ; there 

 is added to these in Polia, Valencinia, and Schizonemertea, a median 

 vessel placed above the digestive tract arising from an anterior lacunar 

 connection between the two lateral spaces beneath the sheath of the 

 proboscis, and partly imbedded in the lower wall of that sheath. The 

 Hoplonemertea possess a looped vessel in the head, which passes anteriorly 

 above the sheath of the proboscis, posteriorly below it, and at this point 

 is connected with three longitudinal vessels, a median, dorsal, and two 

 lateral. Transverse loops connect the three vessels in the region of each 

 dorso-ventral set of muscles in Polia, Valencinia, all Schizonemertea, and 

 most Hoplonemertea, The lateral vessels in the body lie below the level 

 of the lateral nerves as a rule. In Malacobdella the vessels give off branches, 

 especially in the head and posteriorly into the sucker. The blood spaces 

 are filled with a liquid containing, in some cases at least, corpuscles, which 

 are oval and red with haemoglobin in Drepanophorus. The existence of 

 nephridia has not been demonstrated in Cephalothrix and some other 

 Nemerteans. They are present, however, in many, probably in all. They 

 are two in number, one on each side, placed anteriorly. Each organ 



1 Salensky regards it from its mode of development as the homologue of the proboscis of some 

 Turbellaria, which is really the invaginated apex of the body. See papers on Pilidium and 

 Monopora, cited p. 641. 



