106 



frem, og, sees Dyret fra Bugsiden, lader ogsaa ' 

 Coxallappene sig tydeligt adskille. Be sammensatte 

 Oiiie er nu rykkede nær sammen, og i den periphere 

 Area har allerede Synselementerne begyndt at danne 

 sig. Larven bevæger sig om i Våndet paa fuld- 

 kommen samme Maade som i tidligere Stadier. Be- 

 vægelsen tilveiebringes liovedsageligt ved 2det Par 

 Folere eller Aarerne, ved hvis rliytmiske Slag for- 

 fra bagtil Legemet drives frem gjennem Våndet paa j 

 en eiendommelig stodvis Maade. Ved hvert Slag af 

 Aarerne fores deres basale indadkrummede Fortsats I 

 ind mellem Overlæben og Kroppen, saa at de 2 

 bør.steformige Spidser kommer i Contact med Mund- , 

 regionen, og det synes derfor som om denne Fort- 

 sats har en væsentlig Betydning ved Næringsopta- 

 gelsen. Larvetilstanden er nu endt, og med den 

 umiddelbart folgende Hudskiftning begynder den 

 2den Periode i Dyrets Udvikling, den postlarvale 

 Tilstand. 



Postlarval Udvikling. — Fig. 8, 9 fremstiller 

 Iste postlarvale Stadium, livilket folger umiddelbart 

 paa det ovenfor beskrevne sidste Larvestadium, idet 

 , kTin en enkelt Hudskiftning betegner Grændsen 

 mellem begge. Og dog viser Dyret nu et totalt 

 forskjelligt Udseende, ligesom dets Maade at bevæge 

 sig paa er meget afvigende. Man liar nu ikke syn- 

 derlig Vanskelighed ved i det at erkjende en ung 

 Limnadia, skjondt der endnu er till)age nogle Spor 

 fra Larvetilstanden. Hvad der væsentlig charac- 

 teriserer dette Stadium ligeoverfor Larvestadierne, 

 er den betydelige Udvikling af Rygskjoldet, som mi 

 har omformet sig til en tydeligt tveklappet Skal, 

 der bedækker Storsteparten af Legemet, ikke blot 

 oventil, men ogsaa til Siderne. Skallen er dog 

 endnu ikke saa stor, at Legemet kan fuldstændig 

 inddrages i samme, saaledes som Tilfældet er med 

 fuldt udviklede Exemplarer, og Hovedet, ligesom 

 ogsaa Halen er derfor altid ubedækkede. En anden 

 væsentlig Forandring bestaar i Reductiouen af Man- 

 dibularfodderne og den fuldstændige Mangel af de 

 2 fra Aarernes Skaft udgaaende liagudboiede Fort- 

 satser. Endelig maa anfores som en væsentlig Cha- 

 racter, at de hos Larven fuldkommen ubevægelige 

 Branchialfodder nu er traadt i Virksomhed, \u\- 

 forende sine rhytmiske svingende Bevægelser. Læng- 

 den af Legemet, maalt fra Panden til Enden af 

 Haleklorne er 1,14 mm , eller noiagtig den samme 

 som hos Larven i sidste Stadium. Men medens Skal- 

 len hos dette sidste Stadium kun var 0,40 mm. lang 

 _og nep])e niei'e end halvt saa lioi, har den nu en 

 Længde af 0,70 mm. <ig en Hoide af 0,(10 mm. Den 

 er ganske klar og gjennemsigtig, uden Sjior af de 

 hos voxne Exemplarer forekommende concentriske 

 Linier, ligesom Formen er iioget afvigende. Seet 

 fra Siden (se Fig. il) viser den en uregelmæssig af- 



legs, short bristles have already begun to shoot 

 forth, and when the animal is seen from the ventral 

 surface, the coxal lobes may also be distinguished 

 clearly. The compound eyes luive now moved close 

 togetlier, a)ul in the periphei-al area tlie visual ele- 

 ments have already begun to form. The larva 

 moves about in the water in exactly the same man- 

 ner as in the earlier stages. Tlie movement is 

 brought about chiefly liy the 2nd pair of antennæ 

 or the oars, by wliose rhytlimical strokes from front 

 to back the Ijody is propelled through the water in 

 a ])eruliar, jerky manner. At each stroke of the 

 oars, their liasal, incurved projection is carried in 

 between the labrum and the liody, so that the 

 2 bristle-like points are lirought into contact with 

 the oral region. It therefore seems as though tliis 

 projection was of essential importance in tlie admis- 

 sion of food. The larval condition is now termi- 

 nated, and with the immediately succeeding exuvia- 

 tion begins the 2nd period in the animal's develop- 

 ment, the post-larval condition. 



Post-larval Development — Figs. S and repre- 

 sent the tirst post-larval stage, which follows imme- 

 diately after the above-described last larval stage, 

 only a single exuviation marking the lioundary be- 

 tween the two. And yet the animal now presents 

 a totally different appearance, its manner of moving 

 being also very diiferent. There is very little difti- 

 culty now in recognising in it a young Limnadia, 

 although there are still some traces left of its larval 

 condition. What ]irinci])ally characterises tliis stage 

 as compared witli the larval stages is the consider- 

 able development of the carapace whicli is now 

 transformed into a distinctly l)i-valved sliell, cover- 

 ing the greater part of the body, not onl\' above, 

 but also at the sides. Tlie shell, however, is not yet 

 so lai-ge as to allow of the body being completely 

 withdrawn into it, as is the case with fully deve- 

 loped animals; the head therefore, and the tail are 

 always uncovered. Anotlier essential change con- 

 sists in the reduction of the mandibixlar legs and 

 the total absence of tlie 2 backward-curved projec- 

 tions from the scape of the oars. Lastly, it must 

 be mentioned as an essential character that the 

 unite immovable branchial legs in the larva have 

 now begun to act by performing their rhythmical, 

 swinging movements. The length of the body, mea- 

 sured from the frontal jiart to tlie end of the caudal 

 claws is 1.14 mm., or exactly the same as that of 

 the larva in the last stage. But while thr slirll in 

 that stage was only 0.40 mm. long, and scarcely more 

 than half as high, it now has a length of 0.70 mm. 

 and a height of 0.60 mm. It is quite (dear and trans])a- 

 rent, witliout a trace ot the concentric lines occurring 

 in fullgruwn animals, and the shape is somewhat diti'e- 

 rent. Seen fr(jm the side (see hg. ',»), it shows an irre- 

 gular, rounded shape, witli the upper margin where the 



