57 



eller i Juli Manned, at man lios os ialmindeliglied 

 tinder denne Form fuldt udviklet. Jeg liar paa 

 denne Tid observeret den i store Mængder i »Smaa- 

 Tjern jiaa iJovres Hoideidateau, Øst af Jerkin. Som 

 Tilfældet synes at være med de fleste Phyllopoder, 

 naar den temmelig tidligt, og længe for den er fuldt 

 ixdvoxet, Kjonsmodenlied. De storste Individer tin- 

 der man derfor ialmindeliglied længere ud jiaa Ho- 

 sten, medens Stoi'relsen forst paa Sommeren er be- 

 tj'delig ringere. Ofte er der ogsaa paa samme Tid 

 adskillig Forskjel i Storrelsen i forskjellige nær- 

 liggende Tjern. I samme Tjern finder man derimod 

 i Regelen alle individer omtrent ens ndviklede og 

 af ens Farve. 



Det er et meget livligt Dyr. som er i uaflirudt 

 Bevægelse, oftest mere eller mindre nær Overfladen 

 af Våndet. Bevægel.sen tilveiebringes hovedsageligt 

 ved Branchialfoddernes Svingninger, der foregaar 

 paa en meget regelmæssig og elegant Maade, idet 

 de ikke sker noiagtig samtidigt for alle Fodders 

 Vedkommende men successivt, livad 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 

 Ivopulation. idet Hannen med sine Gribeantenner 

 fast omslutter Hunnens Genitalsegment fra Ryggen 

 af, og saaledes kan liegge Individer svømme 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 anfort, onigives 



O' 'O 



af sin Skal. 



Dyrets Fode synes hovedsagelig'. at beståa af 

 mikroskopiske Alger og andre Plantedele, tildels vel 

 ogsaa af Infusorier, der ved Brancliialfoddernes Spil 

 hvirvles ind mod Munden. 



Udbredning. — Nærværende Phyllopode er forst 

 beskrevet fra Gronland, hvor den sj-nes at være 

 meget almindelig, og er senei'e Ideven gjenfunden 

 paa flere andre Steder, saaledes det arktiske Ame- 

 rika, paa Spitsbergen, Xovaja Semlja, Ivolahalvoen 

 og i Sibirieii. Idethele falder dens Udbredning, naar 

 undtages det oveniuevnte Findested i Norge paa 

 Dovres Hoideplateau, udelukkende indenfor den ark- 

 tiske Zone, og dens F(.irekomst her synes at stemple 

 den som en æg^e arktisk og eireumpolar Form. 



or July that this form is generally found fully 

 developeil here. At that season I have observed 

 it in great numljers in small lakes on the high 

 plateau of the Dovre Mountains, east of Jerkin. 

 As seems to be the ease with most Phyllopoda. it 

 attains sexual maturity tolerably early, and long- 

 before it is fully grown. The largest .specimens are 

 therefore generally found later in the autumn, while 

 the size in the beginning of the summer is verj' 

 much smaller. There is also often considerable 

 difl'erence in their size in diiferent 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 graceful manner, not 

 quite simultaneou.sly with all the legs, lint succes- 

 sively, thereby imparting to the movement a peculi- 

 arl\' undulatory effect. The motion thus produced 

 is equable and in a horizcnital direction, the back 

 of the animal being always turned downwards. It 

 may, however, make all kinds of springs in the 

 water, turning and twisting iu 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 mav 

 swim about 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 ()var\- into the 

 base of the marsupium, 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 the mouth by tlie movement of the bran- 

 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 distrilnition, 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 circumjiolar form. 



G. 0. Sars ■ Fauna Norveffiæ. 



