640 THE ANIMAL KINGDOM. 



consists in Carinella of a tube lying close to the blood-vessel, into which 

 it opens in front and behind, and of a spongy (?) gland lying in the wall of 

 the blood-vessel and connected from place to place with the tube. The 

 nephridial tube of Carinoma has three connections to the blood-vessel. 

 It is itself lined by glandular cells. In other Nemerteans it is wholly 

 independent of the blood-spaces, though it may lie in the lacuna at the 

 side of the oesophagus in Schizonemertea. It is branched to a greater 

 or less degree in the Hoplonemertea. The nephridial cells are ciliated 

 in Carinoma, Valencinia, and possibly in others. There is a single duct 

 to each organ in Carinella^ Carinoma, Cerebratulus, Langia, most Hoplo- 

 nemertea ; a large number in Polia, Valencinia,- Lineus, Amphiporus 

 lactifloreus. The duct, whether single or multiple, opens above the level 

 of the lateral nerve. 



The sexes are separate in nearly all instances. Geonemertes palaensis^ 

 Tetrastemma ( = Borlasia) hermaphroditica^ T. {-=B?)Kefersteiniizxt herma- 

 phrodite. The sexual glands are placed in a series on each side of the intes- 

 tine, one in each set of dorso-ventral muscles. They have at first no external 

 opening, but during the evolution of the genital products approach the 

 surface and finally open by a dorsally directed pore. Monopora vivipara, 

 Prosorhochmus ClaparMii, Tetrastemma obscurum, are viviparous forms. 

 The ova are contained in capsules and laid in mucus in some Schizo- 

 nemertea. Development is direct in Cephalothrix, viviparous forms, and 

 Hoplonemertea; or in Schizonemertea accompanied by a metamorphosis. 

 The genus Linens has a creeping ciliated larva, the larva of Desor \ others 

 have a ciliated pelagic helmet-shaped larva, the Pilidium \ 



The majority of Nemertea are marine. Many are capable of swimming. 

 Pelagonemertes is pelagic. Two or three fresh-water forms are known, 

 e.g. Tetrastemma aquarum dulcium from N. America ; and four terrestrial, 

 Tetrastemma agricola (Bermudas) ; T. Rodericanum (Rodriguez Is.) ; Geo- 



1 The larva of Desor is probably not so primitive a form as the Pilidium. The latter, accord- 

 ing to Salensky, has an apical groove in which the ectoderm cells are thickened, probably repre- 

 senting the apical thickening of the Trochosphere. It has a provisional nervous system along the 

 ciliated edges of the side lappets, besides various muscles. It has an oesophagus and stomach. In 

 Desor's larva and the Pilidium alike, the larval epiblast is discarded after it has given origin to the 

 ectoderm of the adult. As to the origin of the principal organs, the nervous is of ectodermic origin 

 (Salensky), of mesodermic (Hubrecht). The ciliated cavities of the brain are derived from invagina- 

 tions of the primary epiblast, which close and afterwards acquire an opening. The two oesophageal 

 outgrowths which were supposed to give origin to the ciliated cavities, probably form the nephridia 

 (Hubrecht). The proboscis is formed by an ingrowth at first solid (Monopora), or an invagination 

 of the secondary (Salensky) or primary (Hubrecht) epiblast. Its muscular walls and sheath are 

 formed from the same mesoblastic rudiment; the proboscis cavity by a split in the rudiment 

 (Salensky) ; or the cavity represents a part of the archicoele (note, p. 636), and the muscular walls and 

 sheath have separate mesoblastic rudiments (Hubrecht). The oesophagus of the adult is the first 

 part of the tract in the larva; the intestine as far as the anus its second part, the two being 

 separate (?) parts of the archenteron in the larva of Desor. The generative organs are perhaps 

 derived from the epiblast. 



