NEMEKTINES 



(By A. A. W. Hubrecht, Ph.D., LL.D., Professor of Zoology, University of Utrecht.) 



Classifi- 

 cation. 



"VTEMERTIXES, or NEMEETEANS (Nemertea), is the 

 _1A name of a subdivision of worms, 1 characterized by 

 the ciliation of the skin, by the presence of a retractile 

 proboscis, by the simple arrangement of the generative 

 apparatus, and in certain cases by a peculiar pelagic larval 

 stage to which the name "[liliilium" has been given. Many 

 of them are long thread-shaped or ribbon-shaped animals, 

 more or less cylindrical in transverse section. Even the 

 comparatively shortest species and genera can always be 

 termed elongate, the broadest and shortest of all being 

 the parasitic JIalacobdclla and the pelagic Pelagonemertes. 

 There are no exterior appendages of any kind. The colours 

 are often very bright and varied. They live in the sea, 

 some being common amongst the corals and algse, others 

 hiding in the muddy or sandy bottom, and secreting gelatin- 

 ous tubes ^Yhich ehsheath the body along its whole length. 

 Formerly, they were generally arranged amongst the 

 Platyelminthes as a suborder in the order of the Turbel- 

 larians, to which the name of Rhynckocosla was applied, the 

 other suborders being the Dendrocoela and the Rliabdocxla. 

 With the advance of our knowledge of these lower 

 worms it has been found desirable to separate them 

 from the Turbellarians and to look upon the Nemertea as 

 a seperate phylum of Platyelminthes. Lately the interest 

 in their morphology has increased since it has been 

 advanced (6, 8) 2 that certain points in their organization 

 appear to indicate a remote degree of relationship to the 

 ancestral forms which must have preceded the Chardata (to 

 which the vertebrate animals also belong), and that this 

 relationship is closer than that which exists between those 

 Protochordata and any other group of invertebrate animals. 

 CLASSIFICATION. The Nemertines are subdivided into 

 three suborders : Hoplonemertea, Schizonemertea, and 

 Palseonemertea (5). The (1) Hoplonemertea embrace all 

 the species with a stylet in the proboscis, and also 

 Malacobdella, which has an unarmed proboscis, but 

 which, by the details of its organization and its develop- 

 ment, must certainly be placed here (parasitism may 

 be the cause of its incipient degeneration). The special 

 characters of this suborder may be gathered from the 

 anatomical descriptions hereafter to be given. In those 

 species of which the embryology has been investigated 

 the development was direct. The more common or more 

 important genera are Amphiporus (A. pulcher, British 

 coasts, Mediterranean; A.splendidm, Atlantic), which is 

 comparatively short, Nemertes (N. gracilis, Atlantic and 

 Mediterranean; Jf. antonina, Mediterranean; N. echino- 

 ilinna, Mediterranean), which is long and thread-like, 

 Tetrastemma, Drepanop/iorus (with more complicate arma- 

 ture in the proboscis), Akrostomum, Malacobdella, (2) In 

 the Schizonmertea all those genera and species are united 

 which have deep, longitudinal, lateral cephalic fissures. 

 The development of some (Linens) is characterized by the 



1 Nemertes was a sea nymph, daughter of Nereus and Doris. One 

 of the genera was named Nemertes by Cuvier. 



3 These figures refer to the bibliography at page 88. 



so-called larva of Desor, of others (Cerebratulus) by the 

 curious and characteristic pilidium-Lirva. The princi]>:il 

 genera are Linens (L. longissimus, Atlantic ; L. obscurus), 

 Cerebratulus (C. marginatus, C. bilinentus, both Atlantic 

 and Mediterranean; C.urticans, Mediterranean ; C'.fascio- 

 latus and aurantiacus, C. hepaticus and dohrnii, Medi- 

 terranean ; C. macintoshii, Madeira), Langia (L. formosa), 

 Borlasia (B. elizabethx). (3) Of the Palxonemertea the 

 most typical and most characteristic genera are Cari- 

 nella and Cephalothrix. They differ considerably both 



Fig. 1. 



Fig. 2. 



FIGS. 1, .!. Diagiamsof the organs of a Ncmcrliue, fig. 1 from below, fig. 2 from 

 above. m, mouth ; div, intestinal diverticula ; a, anus; or. ovaries; ", neph- 

 ridia; Br, brain-lobes; In, longitudinal nerve stems; pr, proboscis; ps, pro- 

 boscidian sheath ; p.o., opening for proboscis. 



from Hoplo- and from Schizonemertines, and evidently 

 belong to a lower stage of differentiation. The genera 

 Polia(P. ddineata and P. curta, Mediterranean) and I V> /- 

 cinia are provisionally arranged in this order because, 

 though less primitive, they are not typical representatives 

 of the other two suborders. The development of these 

 species is not at all, or only very superficially, known. For 

 the further characters of the last two suborders see the 

 anatomical description below. 



Another subdivision generally current is that into the 

 Enopla and the Anopla (14). This does not, however, 

 take into sufficient account the primitive and diverging 



