80 



Rygskjoldet er vel udviklet, men forholdsvis 

 mindre hvælvet end hos det voxne Dyr, og har det 

 bagre Indsnit bredere, næsten retvinklet. Den bag 

 Rygskjoldet fremragende Del af Legemet er forholds- 

 vis tj'kkere og mere sammentrængt end hos voxne 

 Individer og rundtom saa tæt besat med fine Pigge, 

 at den faar et laaddent Udseende. Segmenteringen 

 er endnn lidet tydelig og egentlig knn antydet ved 

 de tæt paa hinanden folgende Tværrader af Pigge 

 (se Tab. XIII, Fig. 27). Sidste Segment er dog 

 meget tydeligt begrændset og ved en kj endelig Ind- 

 knibning sondret fra de foranliggende. Det er ogsaa 

 af langt betydeligere Storrelse, og er aabenbart 

 sondret længe før disse. Af Form er det trapezoi- 

 diskt, gradvis udvidet bagtil, og viser de 2 sidestil- 

 lede dorsale Knnder meget tydeligt. De ydre Hjør- 

 ner af Segmentet er bevæbnede med en Tværrad af 

 stærke Pigge. Halepladen er nfuldstændigt udvik- 

 let og kun repræsenteret ved en ubetydelig, i 2 sy- 

 metriske Spidser udgaaende Udvidning af det dor- 

 sale Integument. Haletraadene er endnu ganske 

 korte, neppe mere end Vs saa lange som Legemet, 

 og viser en noget tendannet Form. De er rundt 

 om besatte med fine, tiltr^'kte Pigge, som dog ikke 

 ordner sig i tydelige Tværrader, og har i Spidsen 

 en særdeles lang og 2 korte Pigge. 



De sammensatte Øine (se Fig. 21, o) er for- 

 holdsvis smaa og har endnu ikke Synselementerne 

 tydeligt udviklede. Umiddelbart foran dem sees 

 meget tydeligt det enkle Øie (oe), der næsten er af 

 samme Storrelse som de sammensatte. 



Første Par Følere (Fig. 21, a ') ligner i Ud- 

 seende dem hos det voxne Dyr, men er forholdsvis 

 større, saa at de rager kjendeligt \\å over Pande- 

 randen. De synes endnu ikke at have Lugtepapiller 

 ndviklede, hvorimod en af de apicale Foleborster er 

 af betydelig Længde. 



Andet Par Folere (Fig. 21, a-), hvoraf der hos 

 det voxne Dyr kun er ubetydelige Rudimenter til- 

 bage, er her mægtigt udviklede, dannende et Par 

 kraftige Aarer, ved Hjælp af hvilke Larven bevæ- 

 ger sig raskt om i Våndet paa en eiendommelig 

 stødvis Maade. De er hver sammensat af et stærkt, 

 cylindriskt, ved Basis i flere Led delt Skaft, der paa 

 sin Ende bærer 2 meget ulige udviklede Grene. 

 Den ydre Gren er adskilligt længere end Skaftet, 

 smalt cylindriskt, og delt i 5 tydelige Led, hvoraf 

 det Iste er vel saa langt som de 4 øvrige tilsammen. 

 Hvert Led bærer ved Enden en lang, tæt cilieret 

 Svommeborste. Den indre Gren er meget liden, 

 neppe mere end V» saa lang som Skaftet, 2-leddet, 

 og forsynet i Spidsen med 3 ulige lange cilierede 

 Børster. 



The carapace is well developed, but compara- 

 tively less vaulted than in the full-grown animal, 

 and the posterior emargination is broader and almost 

 rectangular. That part of the body jirojecting 

 be^yond the carapace is comparativeh- sliorter 

 and thicker than in full-grown specimens, and so 

 thickly covered all round with fine spines, as to 

 present a hairy appearance. The segmentation is 

 still very indistinct and really only indicated by 

 the closely succeeding transverse rows of spines (see 

 PI. XIII, fig. 27). The last segment, however, is 

 very distinctly defined, and is separated from those 

 in front of it by a perceptilile contraction; it is also 

 far larger in size, and has evidently Ijeen formed 

 long before they have. Its shape is trapezoidal, 

 gradually widening posteriorly, and it exhibits very 

 distinctly the 2 laterally-situated dorsal protube- 

 rances. The external angles of the segment are 

 armed with a transverse row of strong spines. The 

 caudal lamella is imperfectly developed, and is only 

 represented by a very slight expansion of the dorsal 

 integument, projecting in two .symmetrical points. 

 The caudal filaments are still ([uite short, scarcely 

 more than ^/s of the length of the body, and exhibit 

 a somewhat fusiform sliape. They are set all round 

 with fine, adpressed spines, wliich, however, are not 

 arranged in distinct transverse rows; and at the 

 extremity there is one particularly long spine and 

 2 short ones. 



The compound eyes (see fig. 21, o) are compara- 

 tively small, and the visual elements not yet dis- 

 tinctly developed. Immediately in front of them, 

 the ocellus (oc) is seen very clearly, almost of the 

 same size as the compoiind eyes. 



The first pair of antennæ (Fig. 21, a^) in appear- 

 ance resemble those of the full-grown animal, but 

 are comparatively lai'ger, so that they project per- 

 cejitibly over the frontal margin. They do not as 

 yet seem to have developed olfactory papillæ, Init 

 on the other hand one of the apical sensory bristles 

 is of considerable length. 



The second pair of antennæ (fig. 21, a'") of 

 which there are left only slight rudiments in the 

 fuUgrown animal, are here powerfully developed, 

 constituting a pair of strong oars, by the aid of 

 which, the larva moves rapidly through the water 

 in a peculiar, jerk\^ manner. Elacli antenna is com- 

 posed of a strong cylindrical scape, divided at the 

 base into several joints, and carrying at its extre- 

 mity 2 very une(|ually developed rami. The outer 

 ramus is considerably longer than the scape, narrow 

 cylindrical and divided into 5 distinct joints, the 

 first of which is rather longer than the other 4 

 together. Eacli joint bears at its extremity a long, 

 densely-ciliated natatory bristle. The inner ramus 

 is very small, scarcely more than Vs of the length 

 of the scape, is bi-articulated, and furnished at the 



