57 



eller i .Tuli Maaned, at man lios os ialminclelighed 

 finder denne Form fuldt ndviklet. Jeg Lar jiaa 

 denne Tid observeret den i store Mæng-der i Smaa- 

 tjern paa Dovres Høideplateau, Øst af Jerkin. Som 

 Tilfældet synes at være med de fleste Pliyllopoder, 

 naar den temmelig tidligt, og længe før den er fuldt 

 ndvoxet, Kjonsmodenhed. De største Individer fin- 

 der man derfor ialmindeliglied længere nd f)aa Ho- 

 sten, medens Størrelsen først paa Sommeren er be- 

 tydelig ringere. Ofte er der ogsaa paa samme Tid 

 adskillig Forskjel i Størrelsen i forskjellige nær- 

 liggende Tjern. I samme Tjern finder man derimod 

 i Eegelen alle Individer omtrent ens udviklede og 

 af ens Farve. 



Det er et meget livligt Dyr, som er i iiafbrudt 

 Bevægelse, oftest mere eller mindre nær Overfladen 

 af Våndet. Bevægelsen tilveiebringes liovedsageligt 

 ved Branchialføddernes Svingninger, der foregaar 

 paa en meget regelmæssig og elegant Maade, idet 

 de ikke sker noiagtig sam.tidigt for alle Fodders 

 Vedkommende men successivt, hvad der giver Ind- 

 trykket af en eindommelig Undulation i Bevægelsen. 

 Den herved frembragte Lokomotion er en ganske 

 jevn i horizontal Retning, hvorunder Dyret altid 

 vender Ryggen nedad. Dog kan det foretage mange 

 forskjellige Volter i Våndet og dreie og sno sig i 

 alle Retninger, hvorved Halens Bevægelser spiller 

 en væsentlig Rolle. Hanner og Hunner sees ofte i 

 Kopulation, idet Hannen med sine Gribeantenner 

 fast omslutter Hunnens CTenitalsegment fra Ryggen 

 af, og saaledes kau begge Individer svønime om i 

 lange Tider, begge vendende Bugsiden opad. Selve 

 Kopulationsakten har jeg ikke faaet observeret. 

 Rimeligvis afventer Hannen det Øieblik, da de 

 modne Æg fra Ovarierne træder ind |i Basis af 

 Rugesækken, hvor de, som ovenfor anført, omgives 

 af sin Skal. 



Dyrets Fode synes liovedsageligt at beståa af 

 mikroskopiske Alger og andre Plantedele, tildels vel 

 ogsaa af Infusorier, der ved Branchialføddernes Spil 

 hvirvles ind mod Munden. 



Udbredning. — Nærværende Phyllopode er forst 

 beskrevet fra Grønland, hvor den synes at være 

 meget almindelig, og er senere ble ven gjenfunden 

 paa flere andre Steder, saaledes det arktiske Ame- 

 rika, paa Spitsbergen, Novaja Semlja, Kolahalvøen 

 og i Sibirien. Idethele falder dens Udbredning, naar 

 undtages det ovennævnte Findested i Norge paa 

 Dovres Hoideplateau, udeliikkende indenfor den ark- 

 tiske Zone, og dens Forekomst her synes at stemple, 

 den som en ægte arktisk og circumpolar Form. 



or July that this form is generally found fully 

 developed here. At that season I have observed 

 it in great numbers in small lakes on the high 

 plateau of the Dovre Mountains, east of Jerkin. 

 As seems to be the case with most Phyllopoda, it 

 attains sexual maturity tolerably eai'ly, and long- 

 before it is fully grown. The large.st specimens are 

 therefore generally found later in the autumn, while 

 the size in the beginning of the summer is very 

 much smaller. There is also often considerable 

 difference in their size in difli'ei-ent lakes, while on 

 the other hand, all the animals in one lake are, as 

 a rule, uniformly developed, and uniform in colour. 



It is a very lively animal, and in constant 

 motion, generally more or less near the surface of 

 the water. The movement is chiefly brought about 

 by the vibrations of the branchial legs, which take 

 place in a very regular and gTaceful manner, not 

 quite simultaneousljr with all the legs, but succes- 

 sively, thereby imparting to the movement a peculi- 

 arly undulatory eifect. The motion thus produced 

 is equable and in a horizontal direction, the back 

 of the animal being always turned downwards. It 

 may, however, make all kinds of springs in the 

 water', turning and twisting in every direction, the 

 movements of the tail playing an important part in 

 these evolutions. Males and females are often seen 

 in copulation, the male, with his prehensile antennæ, 

 firmly embracing the female's genital segment from 

 the back, and in this manner both animals may 

 swim aljout for a long time with the ventral side 

 uppermost. The act of copulation itself, I have not 

 witnessed. The male probably awaits the moment 

 when the mature ova enter from the ovary into the 

 base of the mar.supium, where, as previously stated, 

 they are enveloped in their shell. 



The food of this animal seems to consist prin- 

 cipally of microscopic algæ and portions of other 

 plants, partly also of infusoria, which are swept in 

 towards tlie mouth by the movement of the In-an- 

 chial legs. 



Distribution. — The present Phyllopod was first 

 described from Greenland, where it seems to be 

 very common, and has since been found in several 

 other places, e. g. arctic America, Spitzbergen, 

 Novaia Zemlia, the Kola Peninsula and in Siberia. 

 Altogether its distriljution, with the exception of 

 the above-named place in Norway, on the high pla- 

 teau of the Dovre Mountains, is exclusively within 

 the arctic zone, and its occurrence there seems to 

 stamp it as a true arctic and circumpolar form. 



8 — G. 0. Sars ; Fauna Norvegla'. 



