106 



frem, og, sees Dyret fra Bugsiden, lader ogsaa 

 Coxallappene sig tydeligt adskille. De sammensatte 

 Øiiie er nu rykkede nær sammen, og i den peripkere 

 Area kar allerede Synselementerne begyndt at danne 

 sig. Larven bevæger sig om i Våndet paa fuld- 

 kommen samme Maade som i tidligere Stadier. Be- 

 vægelsen tilveiebringes kovedsageligt ved 2det Par 

 Folere eller Aarerne, ved hvis rkytmiske Slag for- 

 fra bagtil Legemet drives frem gjennem Våndet paa 

 en eiendommelig stodvis Maade. Ved hvert Slag af 

 Aarerne fores deres basale indadkrummede Fortsats 

 ind mellem Overlæben og Kroppen, saa at de 2 

 borsteformige Spidser kommer i Contact med Mund- 

 regionen, og det sj'nes derfor som om denne Fort- 

 sats har en væsentlig Betydning ved Næringsopta- 

 gelsen. Larvetilstanden er nu endt, og med den 

 umiddelbart folgende Hudskiftning beg3'nder den 

 2den Periode i Dyrets Udvikling, den postlarvale 

 Tilstand. 



Postlarval Udvikling. — Fig. 8, 9 fremstiller 

 Iste postlarvale Stadium, hvilket folger umiddelbart 

 paa det ovenfor beskrevne sidste Larvestadium, idet 

 kim en enkelt Hudskiftning betegner Gx-ændsen 

 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 tilbage nogle Spor 

 fra Larvetilstanden. Hvad der væsentlig charac- 

 teriserer dette Stadii;m ligeoverfor Larvestadierne, 

 er den betydelige Udvikling af Pygskjoldet, som nu 

 har omformet sig til en tydeligt tveklappet Skal, 

 der bedækker Størsteparten 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 Reductionen af Man- 

 dibularfodderne og den fuldstændige Mangel af de 

 2 fra Aarernes Skaft udgaaende bagudboiede Fort- 

 satser. Endelig maa anfores som en væsentlig Clia- 

 racter, at de hos Larven fuldkommen i^bevægelige 

 Branchialfodder nu er traadt i Virksomhed, ud- 

 forende sine rh3'tmiske .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 neppe mere end halvt saa hoi, har den nu en 

 Længde af 0,70 mm. og en Hoide af 0,60 mm. Den 

 er ganske klar og gjennemsigtig, uden Spor af de 

 hos voxne Exemplarer forekommende concentriske 

 Linier, ligesom Formen er noget afvigende. Seet 

 ira Siden (se Fig. 9) viser den en uregelmæssig af- 



legs, short bristles have already begun to shoot 

 forth, and when the animal is seen from the venti-al 

 surface, the coxal lobes may also be distinguished 

 clearly. The compound eyes have now moved close 

 together, and in the peripheral area the 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. The movement is 

 brought about chiefly by the 2nd pair of antennæ 

 or the oars, by whose rhythmical strokes from front 

 to back the body is propelled through the water in 

 a peculiar, jerky manner. At each stroke of the 

 oars, their basal, incurved projection is carried in 

 between the labrum and the body, so that the 

 2 bristle-like points are brought into contact with, 

 the oral region. It therefore seems as though this 

 projection was of essential importance in the 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. 8 and 9 repre- 

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

 diately after the above-described last larval stage, 

 only a single exuviation marking the boundary be- 

 tween the two. And yet the animal now presents 

 a totally different appearance, its manner of moving 

 being also very different. There is very little diffi- i 

 culty now in recognising in it a yoiiug Limnadia, ' 

 althoxigh there are still some traces left of its larval 

 condition. What principally characterises this stage 

 as compared with the larval stages is the consider- 

 able development of the carapace which is now 

 transformed into a distinctly bi-valved shell, covei'- 

 ing the greater part of the body, not only above, 

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

 so large as to allow of the bod\^ being completely 

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

 loped animals ; the head therefore, and the tail are 

 always uncovered. Another essential change con- 

 sists in the reduction of tlie mandibular legs and 

 the total absence of the 2 backward-curved projec- 

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

 be mentioned as an essential character that the 

 i[uite immovable branchial legs in the larva have 

 now begun to act by performing their rhythmical, 

 swinging movements. The length of the l)ody, mea- 

 sured from the frontal part to the end of the caudal 

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

 the larva in the last stage. But while the shell 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 clear and transpa- 

 rent, without a trace of the concentric lines occurring 

 in fiiUgrown animals, and the shape is somewhat diffe- 

 rent. Seen from the side (see fig. 9), it shows an irre- 

 gular, rounded shape, with the upper margin where the 



