106 



frem, og, sees Dyret tra Bugsiden, lader ogsaa 

 Coxallappene sig tydeligt adskille. De sammensatte 

 Øine er nu rykkede nær sammen, og i den peripliere 

 Area har allerede Synselementerne begyndt at danne 

 sig. Larven bevæger sig om i A^andet paa fuld- 

 kommen samme Maade som i tidligere Stadier. Be- 

 vægelsen tilveiebringes hovedsageligt ved 2det Par 

 Folere eller Aarerne, ved livis rhytmiske Slag for- 

 fra bagtil Legemet drives frem gjennem Våndet paa 

 en eiendommelig .stedvis Maade. Ved hvert Slag af 

 Aarerne fores deres basale indadkrnmmede Fortsats 

 ind mellem Overlæben og Kroppen, saa at de 2 

 borsteformige Spidser kommer i Contact med Mimd- 

 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, hvilket folger umiddelbart 

 paa det ovenfor beskrevne sid.ste Larvestadium, idet 

 ku.n en enkelt Hudskiftning betegner (jrrændsen 

 mellem begge. Og dog viser Dyret nu et totalt 

 forskjelligt Ud.seende, ligesom dets Maade at bevæge 

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

 derlig Vanskelighed ved i det at erkjende en ung 

 Limnadia, skjondt der endnii er tilbage nogle Spor 

 fra Larvetilstanden. Hvad der væsentlig charac- 

 teriserer dette Stadiiim ligeoverfor Larvestadierne, 

 er den betydelige Udvikling af Ryg-skjoldet, som nu 

 har omformet sig til en tydeligt tveklapptet Skal, 

 der bedækker Størsteparten af Legemet, ikke Ijlot 

 oventil, meit ogsaa til Siderne. Skallen er dog 

 endnu ikke saa stor, at Legemet kau 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- 

 dibularfoddenie og den fuldstændige Mangel af de 

 2 fra Aarernes Skaft udgaaende Ijagudboiede Fort- 

 satser. Endelig maa anføres som en væsentlig Cha- 

 racter, at de hos Larven fuldkominen ubevægelige 

 Branchialfodder nu er traadt i Virksomhed, ud- 

 førende 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 lios dette aidste Stadium knn var 0,40 mm. laue: 

 og neppe mere end halvt saa hoi, har den nu en 

 Længde af 0,70 mm. (jg en Hoide af 0,(iO mm. Den 

 er ganske klar og gjenuemsigtig, uden S])or af de 

 hos voxne Exemplarer forekommende concentriske 

 Linier, ligesom Formen er noget afvigende. Seet 

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



legs, short bi'istles have already begun to shout 

 forth, and when the animal is seen from tlie ventral 

 surface, the coxal lobes may also be distinguished 

 clearly. The compound eyes have now moved dose 

 together, aiul 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 sta.ges. The movement is 

 brought about chiefly liy the 2nd pair of antennæ 

 or the oars, by whose rhythmical strokes from front 

 to back the body is pro]ielled 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 liody. so that the 

 2 bristle-like points are brought into contact with 

 the oral region. It therefore seem.s as thongli this 

 projection was of essential importance in the admis- 

 sion of food. The larval condition is now termi- 

 nated, and witli the immediately succeeding exuvia- 

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

 ment, tlip jiost-larval condition. 



Post-larval Development — Figs. 8 and U repre- 

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

 diately after tlie above-described last larval stage, 

 only a single exuviation marking the boundary be- 

 tween the two. And yet the aniinal now presents 

 a totally different appearance, its manner of moving- 

 being also very different. There is very little diffi- 

 culty now in recognising in it a young Limnadia, 

 although there are still some traces left of its larval 

 condition. What principally characterises this stage 

 as compared with the larval stages is tlie consider- 

 able development of the carapace which is now 

 transformed into a distinctly bi-valved shell, cover- 

 ing the greater part of the body, not only al)ove, 

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

 so large as to allow of the body being completeh'- 

 withdrawn into it, as is the case witli fnlly deve- 

 loped animals; the head therefore, and the tail are 

 always uncovered. Another essential change con- 

 sists in the redu(^tion of the mandibular legs and 

 the total absence of tlie 2 backward-curved projec- 

 tions from the scape of the oars. Lastly, it mu.st 

 be mentioned as an essential character that the 

 (|uite 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 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 

 tliat 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 fallgrown animals, and the sha])e is somewhat diff'e- 

 rent. Seen from the side (sec fig. U), it shows an irre- 

 gular, rounded shM|ic, with the irpjjcr margin where the 



