41 



Gen. Perigonimus. M. Sårs.* 

 Syn. : Rhizoragium. M. Surs. 



Trophosome. Hydraiitlier spindelfonnige mod truad- 

 forniige Tentakler — tilnærmelsesvis i en Kreds ond^ring 

 Hydrantliens tykkeste Parti — siddende eller tæstet ved 

 en kortere eller længore Stilk til krybende Hydrorhiza 

 eller opretstaaende Kiiizocaulora. 



Gonosome. Medusoide Gonoforer sidder i Enden af 

 egne Stilke, der ndgaar fra Hydrorhiza. Rhizdcauloni eller 

 Hydrocaulns. 



Dannelsen af Khizocauloni. tier er paavist ixi Schneider 

 hos Arter af Slægten Lafoea, viser sig i sin enkleste Form 

 og meget tydeligt hos to norske Arter af Slægten Perigo- 

 nimus, nemlig hos P. wuscoides, /isl. Sårs og hos P. sarsii, 

 n. sp., og en begyndende og meget illustrerende Rhizocau- 

 lom dannelse ser man af og til ogsaa hos P. robens, M. 

 Sårs. Denne Art optræder næsten altid med en krybende 

 Hydrorhiza. udbredt over Stilke af T. indirisa og andre 

 Ting; men jeg har havt Anledning til at se, hvorledes flere 

 Ror af denne kryliende Stolo. hvis de paa en eller anden 

 Maade mister sit Underlag, kan slutte sig sammen og saa 

 at sige krybe henad hverandre. Medens det kun er und- 

 tagelsesvis, at saadanne Dannelser forekommer hos P roseils, 

 er det hos P. nmscoides og P. sarsii det normale Forhold. 

 Naar man betragter Kolonier af disse Arter, er det strax 

 paafaldende. hvad Sclnieider ogsaa har gjort opmerksom 

 paa for Lafoikis vedkommende, at Forgreningen ikke sker 

 efter nogensomhelst Lov, Grenene udgaar ikke i noget 

 Afliængighedsforhold til Hydranther, deres Udgangsvinkler 

 varierer umaadelig, hos P. sarsii sees ingen Hydranth i 

 Enden af Grenene, mon spredt uden nogensomhelst Regel- 

 raæssighed over hele Kolonien. En saadan Mangel paa 

 Lovmæssighed i Forgreningen existerer ikke hos nogen 

 Hydroide med almindelig udviklet Hydrocaulns og jeg linder 

 intet naturstridigt i den Tanke, at disse Kolonier er op- 

 staaet ved at forskjellige Ror af Hydrorhiza har sluttet 

 sig sammen, paa samme Maade som vi saa det hos P 

 rosetts, og saaledes har dannet et opretstaaende Rhizocau- 

 lom, i Lighed med det, som Schneider har paavist hos 

 Lafoea. ' 



Perigonimus repens, Wright. 



Trophosome. Hyilrocaulus svagt forgrenet, 3 — 6 mm. 

 hoi. stiger o\) fra en i-eticular krybende Hydrorhiza. Peri- 

 sarc blod, rynket, udvides distalt til et Bæger, der om- 

 slutter Hydranthens nederste Del. Hydranthen har 4 — 12 

 Tentakler, der holdes vexelvis rettet op og ned. 



Gonosome. Gonoforer næsten siddende paa Hydro- 

 caulus, ndvikler sig; til fri Meduser, med 4 Radialkanaler 

 og 4 Tentakler, af livilke to diametralt modsatte er længer 

 end de to andre. 



Findested. En ganske liden Koloni af denne Art 

 blev funden sammen med Plmmdaria ndrru paa St. lU. 



Gen. Perigonimus, M. Sårs. 

 Syn.: Rhizoragium, M. Sårs. 



Trophosome. Hydranths spindle-shaped witb iiliforni 

 tentacles ranged approximately in a circle round the 

 thickest part of the hydranth, sessile or attached by a 

 stem of varying lengt h to tiie creeping hydrorhiza, or ereet 

 rhizocaulom. 



Gonosome. Medusoid gonophores at tlie ends (jf 

 small stems. attaehed to hydrorhiza, riiizocauluin or hydro- 

 caulns. 



The formation of tiie rhizocaulom, as poiiited out by 

 Sch)ieider in species of the genus Lafoea, appears in its 

 simplest ftn-ni and very distinctly, in two Norwegian spe- 

 cies of the genus Perirjoninms, viz. P iintscoides, M. Sårs, 

 and P sarsii, n. sp., and tiie commencement of a very 

 typical example of rhizocaulom formation is also soen now 

 and again in P rosens, M. Sårs. This species appears 

 alraost always with a creei^ing hydrorhiza, spread over 

 stems of T. indivisa and other tliings: but I have observed 

 iiow several tubes of this creeping stolon, if in some way 

 or other they lose their sub-stratum, may join together 

 and, as it were, creep on one another. Whereas the 

 occurrence of sucli fornnxtions is only exceptional in P 

 rosens, it is the normal condition in P innscoides and P. 

 sarsii. Observation of the colonies of these species inime- 

 diately shows — as Schneider, too, has pointed out witii 

 reference to Lafoea — that the ramification takes place 

 according to no law of any kind, that the branches do 

 not branch out in any dependent relation to the hydranths, 

 that their branching angles are exceedingly vai-iable, and 

 — in P. sarsii — that there is no hydranth at the end 

 of the branches, but that they are scattered entirely without 

 regularity over the whole colony. An absence of all con- 

 formity to law in the ramification such as this does not 

 exist in any hydroiil witli an ordinarily developed hydro- 

 caulns, and I see nothing contrary to nature in the thought 

 that these colonies have originated in the union of several 

 hydrorhiza tubes, as we see it in P rosens, and have thus 

 formed an erect rhizocaulom, similar to that pointed out 

 by Schneider in Lajoea. 



Perigonimus repens, Wright. 



Trophosome. Hydrocaulus slightly ramified, from 3 

 to 6 mm. high, rises from a reticulate creeping hydrorhiza. 

 Perisarc soft, wrinkled, expanding distally into a calyx 

 surrounding the lower portion of the hydranth. The latter 

 has from 4 to 12 tentacles. turned alternately up and down. 



Gonosome. Tiie gonophores are almost sessile on 

 the hydrocaulus. and develope into free medusæ. with 4 

 radial canals and -i tentacles, two of wliich, diametrically 

 opposite to one another. are longer than the other two. 



Locality. A very small colony of this species was 

 tbund together with PlnmnJaria rnhra at Station h). 



Den norske Nordhavsexpedition. Kristine Bonnevie. Hydroidii. 



