112 



sætte sine Æg, h^•ad der sikrer Artens fortsatte 

 Existens, om Forholdene et andet Aar skulde vise 

 sig gunstige for en ny Generations Udvikling. Som 

 Eegel synes det dog at være et meget lidet Procent- 

 tal af de utallige Larver, som i Begyndelsen ud- 

 klækkes, der virkelig kommer til fuld Udvikling. 

 Larver og Unger finder man uden Forskjel overalt 

 i de Vandansanilinger, hvori de træffes, lige saa 

 hyppigt tæt inde ved Bredden som ude paa dybere 

 Vand. Anderledes er det med fuldvoxne Exempla- 

 rer. Disse holder i Regelen kun til paa de dybeste 

 Steder af Dammen og her gjerne nær Bunden. Da 

 Dyrene i Regelen er meget gjennemsigtige, er det 

 ikke saa godt at faa Øie paa dem fra Stranden af. 

 Dog vil ialmindelighed den ojiake gulbrune Æg- 

 masse forraade dem, navnlig naar Bunden, henover 

 hvilken de bevæger sig, bestaar af morkt Mudder. 

 Bevægelsen er ikke synderlig hurtig og har Cha- 

 racteren af et forholdsvis sagte og noget ujevnt 

 Lob, hvorunder i Regelen Ryggen vender opad. 

 Holdte i Aijuarier kan man noiere studere deres 

 Bevægelser og øvrige Levevis. Der kan ikke være 

 nogen Tvivl om, at Dyrets hovedsageligste Be- 

 vægelsesorganer er Aarerne. Det er ved hurtigt 

 gjentagne Slag til Siderne af disse Lemmers ydre 

 Parti, at Legemet bliver drevet igjennem Våndet, 

 skjondt ogsaa Branchialfoddernes Svingninger tor 

 til en vis (Irad understøtte Bevægelsen. Støder 

 Dyret under sine Bevægelser paa tætte Conferve- 

 masser, formaar det med stor Behændighed at ar- 

 beide sig igjennem dem, hvorved den meget bevæge- 

 -lige Bagkrop .spiller en A'igtig Rolle. Idethele sees 

 D_yT.-et meget ofte at foretage energiske Boininger 

 og Strækninger af denne Del af Legemet, dels for 

 at overvinde Hindringer for dets Passage gjennem 

 Våndet, dels for at befri det indre af Skallen for 

 fremmede indkomne Partikler. Meget ofte faar man 

 se, at Dyret med Forenden hefter sig fast til de i 

 Våndet værende Grjenstande. navnlig til Undersiden 

 af Blade eller Conferver i Overfladen af Aqvarieme, 

 og forbliver i denne Stilling sædvanligvis i længere 

 Tid. Fastheftningen synes hovedsageligst at tilveie- 

 bringes ved de stærke hageformige Pigge langs For- 

 siden af Aarernes Grene, tildels ogsaa ved det eien- 

 dommelige fra Hovedets Dorsalside udgaaende koUe- 

 formige Appendix, som man ved nøiere Uudersogelse 

 altid vil finde er i umiddelbar Contact med den 

 Gjenstand, hvortil Dyret er fastklamret. Dyret er 

 herunder ikke i absolut Ro, men der foregaar en 

 svag rhj-tmisk Svingning af hele Legemet frem og 

 tilbage, aabenbart foraarsaget ved de heftigt bevæ- 

 gede Branchialfødder. Disse Svingninger sker paa 

 fuldkommen samme Maade som hos Branchipodiderne, 

 idet de ikke er simultane men successive, hvad der 

 giver Indtr^-kket af en eiendommelig grazios Undu- 

 lation i Bevægelsen. Idethele er det meget sjelden 

 at denne s^-ingende Bevægelse af Branchialfodderne 



some, at any rate, of the animals attain to sexual 

 maturity, and are able to deposit their eggs, therel)y 

 ensuring the continued existence of the species, 

 should conditions another year be favorable for the 

 development of a new generation. As a rule, it 

 appears to be a very small percentage of the innu- 

 merable larvæ at first hatched, that really liecome 

 full^• developed. Larvæ and 3'oiing ones are found 

 without distinction all over the pieces of water in 

 which they are met with, ([uite as fre(]uently close 

 to the Ijank as out in deeper water. It is otherwise 

 with fuUgrown animals. They generally keep to 

 the deeper parts of the pond and near the bottom. 

 As the animals are generally very transparent, it 

 is not very easy to see them from the shore. The 

 opaque, yellowish brown mass of eggs, however, will 

 generally betray them, especially if tlie bottom, 

 over which they move, consists of dark mud. The 

 motion is not remarkably quick, but has the clia- 

 racter of a comparatively^ slow and somewhat 

 uneven dart, during which the l)ack is generally 

 uppermost. AVhen kept in an aquarium, its move- 

 ments and other habits may be more carefully stu- 

 died. There can be no doubt that the animal's 

 most important organs of locomotion are the oars. 

 It is by (juickly repeated side-strokes of the 

 distal part of these limbs that the body is driven 

 through the water, although the swinging of the 

 branchial legs may also, to a certain extent, assist 

 the movement. Should the animal, as it moves, 

 come in contact with thick masses of confervæ, it 

 manages with great dexterity to work its way 

 through them, the very mobile hind part of the 

 body plajdng an important part in that proceeding. 

 The animal may often be observed to make ener- 

 getic liends and extensions of this jiart of the Ijody, 

 partly to overcome obstacles to its passage through 

 the water, partly to rid the shell of foreign par- 

 ticles that have entered. The animal may very 

 often be seen to attach itself by its anterior end 

 to objects in the water, especially to the under 

 siu-face of leaves or confervæ on the surface of the 

 aquarium, and generally remain in this position for 

 some time. The attachment appears jirincipallj^ to 

 be eifected by means of the strong, hook-like spines 

 along the front of the rami of the oars, and partly 

 by the peculiar clavate appendage issuing from 

 the dorsal .surface of the head, and which, on close 

 examination, will alwaj'^s be found in immediate 

 contact with tlie object to which the animal is 

 clinging. The animal meanwhile is not absolutely 

 at rest, for there is a slight rhythmical swinging 

 to and fro of the whole body, occasioned by the 

 violent agitation of the branchial legs. These pul- 

 sations take place in exactly the same manner as in 

 the Branchipodidæ, not being simultaneous Ijut suc- 

 cessive, tlius producing the im2ires.?ion of a peculiar, 



