NEMERTEA BNOPLA 643 



teans with the exception of Keptantia and Siboganemertes 

 and in these they developed in different ways.^ As in the 



^ Here seems to be the right place to mention the fact that in one 

 species of Monostilifera the presence of paired rhynchocoelomic diverti- 

 cula is noted by Biirger, i.e. Amphiporus stannii. However, 

 these diverticula are quite other structures, or at least much more primi- 

 tive ; they are present in the nephridial region alone and are very small 

 though wide. The musculature of the rhynchocoelomic cavity widens out 

 at certain places. These are the sacs that have a wide lumen and open 

 with a wide mouth into the rhynchocoelomic cavity. The muscular walls 

 of these sacs are the regular continuations of, and just as thick as, the 

 rhynchocoelomic wall, and a difference of structure seems not to exist. 

 The wall of these diverticula in Polystilifera is as a rule much thinner, 

 even when contracted, and we know that the mouth is provided with 

 a sphincter, that is absent in A. stannii. In some unarmed genera 

 other rhynchocoelomic diverticula, paired and unpaired, exist, but they 

 never are comparable with those of the Polystilifera. Amphiporus 

 stannii is a Monostilifer, as its stylet is well known. In Drepano- 

 phorus valdiviae (Burger), which species has exactly the same 

 rhynchocoelomic diverticula as Amphiporus stannii, the stylet is 

 unknown ; in both species these structures are restricted to the nephridial 

 region, and in other characteristics they are very much alike too : they 

 have no eyes, both possess small cerebral organs without a sac, behind or 

 partly behind the brains, both have lateral nerve-cords (not ventral as in 

 Drepanophorus), both have a layer of glands in the head that fails in all 

 Polystilifera and is present in Amphiporus, both have brains that are 

 quite different from all Polystilifera, with a very small dorsal and larger, 

 perfectly separated ventral ganglia, in both the vascular system differs 

 from that of Poly stiUf era by the presence of a dorsal loop over the brain, 

 &c., &c. Biirger says in his monograph of the Valdivia expedition 

 (9, p. 174) : ' Leider ist aber der Riissel nicht vorhanden, und die Organisa- 

 tion weist einige Ziige auf, die mehr auf Amphiporus als auf Drepano- 

 phorus hindeuten ; indessen ist dieses Stiick dem Genus Drepanophorus 

 zuzurechnen, weil sein Rhynchocolom, wenigstens im vordersten Abschnitt, 

 laterale, einander gegeniiber entspringende seitliche Aussackungen besitzt, 

 die bisher nur von Drepanophorus bekannt sind.' He forgets, however, 

 that he himself described them in 1895 in Amphiporus stannii 

 in the monograph of the Nemerteans of Naples, p. 571, and PI. xvii, 

 figs. 5, 13, and 14. A comparison of these figures with those of the Valdivia 

 (PI. xxxi) gives the striking resemblance of the above-discussed species, 

 which certainly belong to one genus, which I might mention Valdivia- 

 nemertes. The presence of the only stylet in Valdivianemertes 

 stannii (Grube) makes it certain that both V. stannii and V. val- 



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