82 



1 senere Stadier reduceres 2det Pav Folere mere 

 og mei-e og taber tilsidst sine Svommel)orster fuld- 

 stændigt, hvorved deres Betydning som Bevæge- 

 organer er opliort. Bevægelsen overtages nu iide- 

 lukkende af de mere fuldkomment iidviklede Fodder. 

 Halepladen begynder saa smaat at forlænge sig og 

 faar flere Randtoi'ne, men er endnn hos temmelig 

 store Unger meget lideii (se Tab. XIII, Fig. "28). 



Levevis. — Nærværende Phylloiiode synes ikke, 

 som Tilfældet er med de lieste ovrige Former, at 

 være ndelukkende indskrænket til mindre Vand- 

 ansamlinger, som ud paa Sommeren torrer ganske 

 eller delvis nd. Jeg har tvertimod liidtil kun fun- 

 det den i temmelig store og (^ybe Vande, og har 

 seet den paa Dybder af mindst 3 — 4 Favne. Som 

 Regel holder den sig lige ved Bunden og svømmer 

 langs denne, altid med Ryggen o])ad. Men ikke saa 

 .sjelden tager den sig ogsaa Fdflugter hoiere op i 

 Våndet og vender lierunder snart R^'g, snart Bug 

 opad, eller dreier sig rundt paa forskjellig Vis. 

 Svomningen tilveiebringes hos det voxne Dyr itde- 

 hikkende ved Hjælp af Fodderne og foregaav med 

 en ganske jevn og ikke meget hurtig Fart. 



De grovt tandede Kindbakker og de stærke klo- 

 formige Enditer jjaa de forreste Par Fodder tyder 

 paa, at Dyret hovedsageligt lever af Rov, rimeligvis 

 for en stor Del af andre Entomostraceer. .leg har 

 ogsaa ikke sjeldent mellem Fodderne paa dem fun- 

 det Daphnier og forskjellige Copepoder {Cijclops, 

 Helerocope). Efter Sigende skal den i visse Tilfælde 

 ogsaa fortære Fiskerogn og derved blive skadelig 

 for Fiskebestanden i de Vande, hvori den fore- 

 kommer. 



De allerfleste Individer, man træffer, er af Hun- 

 kjon, og det er foi'st efter et meget nøie Eftersyn 

 af talrige Exemplarer, at det er lykkets mig at 

 iinde frem nogle faa Hanner. Efter al Sandsynlig- 

 hed er Hannernes Foi'ekomst lain indskrænket til 

 en ganske kort Periode, rimeligvis til Slutten af 

 Sommeren. 



Forekomst. — Selv har jeg her i Landet kun 

 trutfet den ])aa Filefjelds Hoideplatean, omkring Ny- 

 stuen, dels i selve Nystuvandet eller i Udvidningen 

 af den fra samme mod Ve.st udgaaende Elv, dels i 

 et Fjeldvand, Vesleskartjernet kaldet, paa selve 

 Nystufj eldets Ryg og i en Hoide af circa 4O0O Fod 

 over Havet. T det sidstnaivnte Vand, der er tem- 

 melig dylit, i'andtes den i Slutningen af August 1887 

 i stor Mængdc, og kunde fra Stranden af gjennem 

 det krystalkhire Vand sees overalt paa Bundcni. 

 Kun undtagelsesvis fandtes den saa mer Stranden 

 og paa saa grundt Vand, at den kunde tåges med 

 en almindelig Haand-liaav, og min Fangst af den 

 indskrænkede sig derfor ogsaa, forste (lang, jeg be- 

 sogte dette Vand, kun til nogle faa Exemplai-er. 



In later .stages the 2nd pair of antennæ become 

 more and more reduced in size, and at last entirely 

 lose their natatory bristles, whereby their impor- 

 tance as oi'gans of motion ceases. The production 

 of motion is now undertaken exclusively by the 

 more fully developed legs. The caudal lamina com- 

 mences slightly to lengthen, and ac(|uires several 

 marginal spines, but is still, even in rather large 

 young ones, very small (see PL XIII, fig. 28). 



Habits. — The present Phy 11 opod does not seem, 

 as is the case with most of the other forms, to be 

 exclusively confined to small pieces of water, which 

 either c[uite or partially dry up towards the end 

 of the summer. ()n the contrary, I have hitherto 

 only found it in rather large and deep lakes, and 

 have seen it at dei)ths of at least 3 or 4 fathoms. 

 As a rule, it keeps to the bf}ttom, where it swims 

 along, always with its back u])permost; but it not 

 infre(piently makes excursions higher up in the 

 water, and during these, turns sometimes its back, 

 sometimes its ventral surface uppermo.st, or twists 

 about in various ways. The action of swimming 

 in the full-grown animal is ])erformed exclusively 

 by the aid of the legs, and at a perfectly even, 

 and not very rapid rate. 



Tlie coarsely dentated mandibles, and the strong, 

 claw-like endites of the foremost ])airs of legs indi- 

 cate that this animal lives principally by prej'ing 

 on others, probabl\- to a lai'ge extent on other En- 

 tomostraca. I have also not infrequently found 

 between its legs Dajdmiæ and various Copepods 

 {Cyclops, Heterocope). According to report, it has 

 also, in certain cases, been known to consume fish- 

 spawn, and is thus detrimental to the stock of fish 

 in the lakes where it occurs. 



The greater number of sjiecimens met with are 

 of the female sex, and it is only after a very care- 

 ful examination of nuniei'ous specimens that I have 

 succeeded in finding a few males. In all probability, 

 the occui'rence of the males is limited to ipiite a 

 short period, probably until the end of tlie summer. 



Occurrence. — In this countr\- (Norway) I have 

 personally only met with this form on the high 

 plateau of the Filetjeld. about Xystuen, partly in 

 Nystue Lake itself and the expansions of the river 

 flowing out of it towards the west, and i)artly in a 

 mountain tarn called Vesleskartjern, on the ridge 

 of Nj'stue Mountain, and at a height of about 4000 

 feet above the sea. In the last-named lake which 

 is rather deej», tliis s])ecies was found at the end of 

 August, 1887, in great numbers, and could be seen 

 i'rom the shore, through the clear water, all over 

 the bottom. ()n]\' in exceptional cases was it found 

 so near the shore and in such shallow Avater, that 

 it could be taken with an ordinary hand-net, so 

 that my take of it, the lirst time I visited this lake, 



