115 



Sipuneler 4; medens det hos Slægterne Phascolosoma, 

 Onchnesoma og Tylosoma er snart 4, snart 2 og endelig 

 kun 1. Hvor der kun er 1, kan Basaldelen enten være 

 ganske udelt (Onchnesoma Steenstrupii), eller den kan 

 være delt i 2 eller flere Rødder. Befæstningsstedet er 

 ogsaa underkastet Afvigelser; saaledes findes Retrac- 

 torerne fæstede dels i den forreste, dels midterste, og 

 dels bagerst© Trediedel af Kroppen. 



Saavel hos Sipuneulus, som Phascolosoma, Onchne- 

 soma og Tylosoma ere Muskelfibrene lange, glatte, dels 

 runde, dels mere flade, og vise ved stærk Forstørrelse 

 en fin langsgaaende Stribning. I Musculaturen findes et 

 temmelig stort Antal Kjerner; men disse ere ikke pla- 

 cerede indeni Muskelfibrene, men udenpaa dem, ere til- 

 dels omgivne af en ringe Mængde Protoplasma (Fig. 9 e, e, e), 

 og maa betragtes som excentrisk liggende Muskelkjerner. 

 Lignende Kjerner findes overalt i det mellem Muskel- 

 fibrene tilstedeværende Bindevæv, der danner et Slags 

 Sarcolem, som paa Tversnit faar Udseende af et Netværk, 

 der har en Maske for hver Muskelfiber (Fig. 15 1, 1, 1, 

 Fig. 21 1). Dette Sarcolem hænger sammen med den 

 Hinde (Peritoneum), der beklæder Kropshulheden. Paa 

 isolerede Muskelfibre lader det sig ei afgjøre, hvad der 

 egentlig tilhører Fiberen og hvad Sarcolemmet, da dette 

 ikke paa nogen Maade udhæver sig fra Muskelfiberen. 

 Graber omtaler cellelignende Legemer, som han har fun- 

 det paa Ringmuskellaget, og om hvis Betydning han Intet 

 ved at meddele. Vi skulle være tilbøielige til at tro, at 

 disse Legemer ere de af os paaviste Kjerner med sin 

 Protoplasma-Omgivelse, der tilhører Musculaturen, saafremt 

 de ikke have været fremmede, tilfældige Legemer. 



Keferstein angiver, at paa den indre Flade af Krops- 

 hulheden er Musculaturen beklædt med en fin Membran, 

 hvori han dog ikke med nogen Tydelighed har kunnet 

 opdage Celledannelse *), En saadan Hinde findes saavel 

 hos Slægten Sipuneulus, som hos Slægterne Phascolosoma, 

 Onchnesoma og Tylosoma; men den beklæder ikke alene 

 Kropsmusculaturen, men ogsaa Retractorerne, — hvor den 

 er særdeles stærk, — samt Segmentalorganerne, Spiserøret, 

 Tarmen, M ervestrengen og dennes Grene, saa langt som 

 disse ligge frit i Kropshulheden, og er, som allerede 

 nævnt, sammenhængende med det Muskelfibrene omgi- 

 vende Sarcolem, hvorfra den uden nogen skarp Grændse 

 gaar over i Cutis. Denne fine Membran, som vi herefter 

 ville kalde Peritoneum (Fig. 10 p, p, Fig. 15 p, Fig. 21 p, p), 

 lader sig med temmelig Lethed isolere der, hvor den dæk- 

 ker Musculaturen, og er overalt forsynet med mere 

 eller mindre tætliggende Celler, omgivne af et cilie- 

 bærende Protoplasma (Fig. 4 A, p, p). Paa den tynde gjen- 

 nemsigtige Snabel af Onchnesoma Steenstrupii sees tyde- 

 ligt, hvorledes saavel Hudens Indflade, som Spiserørets, 



l ) Zeitschrift f. w. Zoologie B. XV, Pag. 407. 



Sipunculi known to us, 4; while in the genera Phascolo- 

 soma, Onchnesoma and Tylosoma it is sometimes 4, some- 

 times 2 and even only 1. Where there is only 1, the 

 basal part may either be quite undivided (Onchnesoma 

 Steenstrupii) or it may be divided into 2 or more roots. 

 The point of attachment is also subject to deviations; 

 thus the retractors are found attached partly in the an- 

 terior, partly in the middle, and partly in the posterior 

 third part of the body. 



As well in the Sipuneulus as in the Phascolosoma, 

 Onchnesoma and Tylosoma, the muscular fibres are long, 

 smooth, partly round, partly more flat, and shew, when 

 strongly magnified, a fine longitudinal striation. In the 

 muscular system there appear rather a large number of 

 nuclei; but these are not situated within the muscular 

 fibres, but outside of them; they are partly surrounded 

 by a slight quantity of protoplasma (fig. 9 e, e, e) and must 

 be considered as muscular nuclei in excentric position. 

 Similar nuclei are found everywhere in the connecting 

 tissue, which exists between the muscular fibres, and 

 which forms a sort of sarcolem, having in cross section 

 the appearance of net-work with a mesh for each muscular 

 fibre (fig. 15 1, 1, 1, fig. 21 1). This sarcolem hangs together 

 with the membrane (peritoneum) which lines the peri- 

 visceral cavity. In isolated muscular fibres, one cannot 

 determine what properly belongs to the fibre and what 

 to the sarcolem, as the latter does not in any way 

 distinguish itself from the muscular fibre. Graber men- 

 tions cell-like bodies, which he has found in the layer of 

 annular muscles, and as to the signification of which he 

 is unable to give any information. We are inclined to 

 think that these bodies are the nuclei indicated by us, 

 with a surrounding of protoplasma belonging to the 

 muscles; unless they should have been extraneous or 

 fortuitous substances. 



Keferstein states that the muscles on the interior 

 surface of the perivisceral cavity are covered with a fine 

 membrane, wherein however he has not been able distinctly 

 to discover any cellular formation 1 ). Such a membrane 

 is found as well in the genus Sipuneulus as in the genera 

 Phascolosoma, Onchnesoma and Tylosoma; it does not 

 however cover only the muscles of the body, but also the 

 retractors — where it is especially strong — and the seg- 

 mental organs, the alimentary canal, the intestine, the 

 nervous cord and its branches, as far as these have a 

 free position in the perivisceral cavity; and it is, as al- 

 ready mentioned, continuous with the sarcolein that sur- 

 rounds the muscular fibres proceeding from the same and 

 going over into the cutis, without any sharply defined 

 boundary. This fine membrane, which we shall hereafter 

 call peritoneum (fig. 10 p, p, fig. 15 p, fig. 21 p, p), may be 

 rather easily isolated where it covers the muscles; and it 

 has everywhere more or less closely-lying cells surrounded 

 by a ciliated protoplasma (fig. 4 A, p, p). On the thin trans- 

 parent proboscis of the Onchnesoma Steenstrupii, it may 



') Zeitschrift f. w. Zoologie B. XV, pag. 407. 



