153 



yderligere bestyrkede ved at undersøge andre Arter, der 

 frembøde ligesaa store Afvigelser fra Slægten Phascolo- 

 soma som Ph. Strombi, uden at vi derfor saa nogen 

 Grund til at danne nye Slægter, da Forskellighederne 

 ligesaalidt hos denne som hos hine vare saa væsentlige, 

 at de kunde begrunde Dannelsen af nye Slægter. 



De før nævnte vigtige Punkter, der efter Hr. Théel ud- 

 gjøre det Eiendommelige for Slægten Phaseolion, og hvor- 

 ved den adskiller sig fra Slægterne Sipunculus og Pha- 

 scolosoma ere Følgende: 



Tentaklerne ere trekantede; Snabelen kan indtrækkes 

 lige til Analaabningen, og i den bagerste Kropsende fin- 

 des ingen Aabning i Form af en stor Pore. Kun to Re- 

 tractorer, hvoraf den ventrale, der er den mindste, deler 

 sig ved Basis i to Rødder. Digestionsapparatet danner 

 to Circumvolutioner, der ere mere eller mindre spiral- 

 förmige, og som ere fæstede til Kropshulheden ved mange 

 radiære Muskler. 



Hertil skulle vi bemærke, at Tentaklerne hos Phas- 

 colosoma-Arterne variere overmaade meget saavel i Antal 

 som Form, og have hidtil ikke engang kunnet tjene til 

 paalidelige Artsmærker. At Snabelen trækkes ind til Anal- 

 aabningen, finder temmelig hyppig Sted hos flere Arter, 

 og kan ligesaalidt som Tentaklernes Form være noget 

 sikkert Bestemmende for Arten og endnu mindre for 

 Slægten. At Phaseolion mangler en Aabning i den ba- 

 gerste Kropsende, kan dog vanskeligt være noget Eien- 

 dommeligt for den, da saavel de Arter af Slægten Phas- 

 colosoma og Sipunculus, vi have undersøgt, som af vore 

 nye Slægter lider af den samme Mangel. Og saavidt os 

 bekjendt har endnu ingen Forsker paavist med Sikkerhed 

 den her omtalte Aabning, om hvis Tilværelse, som bekjendt, 

 har været stridt adskilligt. — Retractorerne have vi fun- 

 det meget forskjellige med Hensyn til Udspring, Form og 

 Antal ikke alene hos Slægten Phascolosoma, men ogsaa 

 hos enkelte af vore nye Slægter; men Forskjelligheden 

 hos den enkelte Art, hvor stor den end har været, har 

 dog altid været af en saadan Natur, at vi have kunnet 

 finde Overgange hos nærstaaende Arter, saa at vi vel i 

 en saadan Varieren af Retractorerne have fundet et Hjælpe- 

 middel til yderligere at characterisere Arten, men ingen- 

 lunde noget saa stærkt Eiendommeligt, at vi deraf vovede 

 at grunde en ny Slægt. Og vi tro heller ikke, at Retrac- 

 torernes Antal er noget saa væsentligt, at, naar ikke an- 

 dre vigtigere Særegenheder optræde, man cla ved Hjælp 

 af dem skulde kunne udsondre af Arter nye Slægter. ■ 

 Vi have saaledes seet Phascolosoma-Arter med 4, 2 og 

 1 Retractor, ligesom vi hos vore nye Slægter have dels 

 1 Retractor uden Rødder (Onchnesoma Steenstrupii), dels 

 1 Retractor med lange Rødder (Tylosoma Lütkenii), der 

 ere fæstede paa Dorsal- og Ventralfladen, Dersom vi 

 skulde have ladet os nøie med Skjelneraærker som de 

 af Dr. Théel angivne til Dannelsen af nye Slægter, havde 

 vi visseligen af Ph. squamatum grundet en ny Slægt; thi 

 det staar ikke til at nægte, at denne Art frembyder større 

 Afvigelser end Ph. Strombi; men for os stille Fordrin- 

 gerne til en Slægts Dannelse sig større, idet vi formene, 



further confirmed by examining other species, which exhi- 

 bited quite as great deviations from the genus Phascolo- 

 soma as Ph. Strombi, without finding any reason to form 

 new genera; as the differences were, neither in one case 

 nor in the other, so essential as to warrant the forma- 

 tion of new genera. 



The before named important points, which, according 

 to Mr. Théel, constitute the peculiarities of the genus Phas- 

 eolion, and whereby it is distinguishable from the genera 

 Sipunculus and Phascolosoma, are the following: 



The tentacles are 3 sided; the proboscis can be re- 

 tracted even to the anal aperture, and in the posterior ex- 

 tremity of the body there is no opening in the form of a 

 large pore. Only two retractors, of which the ventral one, 

 which is the smallest, is divided at the base into two 

 roots. The apparatus of digestion forms two circumvolu- 

 tions which are more or less spiral, and which are attached 

 to the perivisceral cavity by many radiary muscles. 



We must here remark that the tentacles in the spe- 

 cies of Phascolosoma vary in an extraordinary degree, 

 as well in number as in form, and have hitherto not even 

 been able to serve as trustworthy specific marks. That 

 the proboscis is drawn in to the anal aperture, is something 

 which occurs rather frequently in several species, and 

 can just as little as the form of the tentacles, be any 

 certain criterion of the species, still less of the genus. 

 That the Phaseolion has no opening in the posterior end 

 of the body, can scarcely be anything peculiar to it; 

 because the species of the genera Phascolosoma and 

 Sipunculus, which we have examined, as well as those of 

 our new genera, have the same deficiency. And so far 

 as we know, there has been yet no naturalist, who has 

 demonstrated with certainty the existence of this opening, 

 about which, as is well known, there has been a good 

 deal of controversy. We have found the retractors dif- 

 fering with respect to their issue, form and number, not 

 only in the genus Phascolosoma, but also in some of 

 our new genera; but the differences in the single species, 

 however great it may have been, has still always been 

 of such a nature as to enable us to find transitions in 

 species closely related; so that such a variation in the 

 retractors has furnished us with auxiliary means of cha- 

 racterising the species more particularly; but we have 

 been far from finding therein anything so strongly peculiar,, 

 as to warrant our venturing to base a new genus thereon. 

 Neither do we think that the number of the retractors 

 is anything so essential, that, when no other more impor- 

 tant peculiarities appear, we should be able thereby to 

 select new genera out of a number of species. We have 

 thus seen species of Phascolosoma with 4, 2 and 1 

 retractor; just as we have, in our new genera, sometimes 

 1 retractor without roots (Onchnesoma Steenstrupii} 

 sometimes 1 retractor with long roots (Tylosoma Lütkenii), 

 attached to the dorsal and ventral surface. If we had 

 been satisfied with the characteristics indicated by Dr. 

 Théel for the establishing of new genera, we should cer- 

 tainly have made a new genus of Ph. squamatum; for it 



