Rygskjoldet er vel udviklet, men forholdsvis 
mindre hvelvet end hos det voxne Dyr,,og har det 
bagre Indsnit bredere, nesten retvinklet. Den bag 
Rygskjoldet fremragende Del af Legemet er forholds- 
vis tykkere og mere sammentrengt end hos voxne 
Individer og rundtom saa tet besat med fine Pigge, 
at den faar et laaddent Udseende. Segmenteringen 
er endnu lidet tydelig og egentlig kun antydet ved 
de tet paa hinanden folgende Tverrader af Pigge 
(se Tab. XIII, Fig. 27). Sidste Segment er dog 
meget tydeligt begrendset og ved en kjendelig Ind- 
knibning sondret fra de foranliggende. Det er ogsaa 
af langt betydeligere Storrelse, og er aabenbart 
sondret lenge for disse. Af Form er det trapezoi- 
diskt, gradvis udvidet bagtil, og viser de 2 sidestil- 
lede dorsale Knuder meget tydeligt. De ydre Hjor- 
ner af Segmentet er bevebnede med en Tverrad af 
sterke Pigge. Halepladen er ufuldsteendigt udvik- 
let og kun repreesenteret ved en ubetydelig, i 2 sy- 
metriske Spidser udgaaende Udvidning af det dor- 
sale Integument. Haletraadene er endnu ganske 
korte, neppe mere end '/s saa lange som Legemet, 
og viser en noget tendannet Form. De er rundt 
om besatte med fine, tiltrykte Pigge, som dog ikke 
ordner sig i tydelige Tverrader, og har i Spidsen 
en seerdeles lang og 2 korte Pigge. 
De sammensatte Mine (se Fig. 21, 0) er for- 
holdsvis smaa og har endnu ikke Synselementerne 
tydeligt udviklede. Umiddelbart foran dem sees 
meget tydeligt det enkle Wie (oc), der nesten er af 
samme Storrelse som de sammensatte. 
Forste Par Folere (Fig. 21, a‘) ligner i Ud- 
seende dem hos det voxne Dyr, men er forholdsvis 
storre, saa at de rager kjendeligt ud over Pande- 
randen. De synes endnu ikke at have Lugtepapiller 
udviklede, hvorimod en af de apicale Foleborster er 
af betydelig Lengde. 
Andet Par Folere (Fig. 21, a*), hvoraf der hos 
det voxne Dyr kun er ubetydelige Rudimenter til- 
bage, er her megtigt udviklede, dannende et Par 
kraftige Aarer, ved Hjelp af hvilke Larven beve- 
ger sig raskt om i Vandet paa en eiendommelig 
stodvis Maade. De er hver sammensat af et stzerkt, 
cylindriskt, ved Basis i flere Led delt Skaft, der paa 
sin Ende berer 2 meget ulige udviklede Grene. 
Den ydre Gren er adskilligt lengere end Skaftet, 
smalt cylindriskt, og delt i 5 tydelige Led, hvoraf 
det iste er vel saa langt som de 4 ovrige tilsammen. 
Hvert Led berer ved Enden en lang, tet cilieret 
Svommeborste. Den indre Gren er meget. liden, 
neppe mere end '/s saa lang som Skaftet, 2-leddet, 
og forsynet i Spidsen med 3 ulige lange cilierede 
Borster. 
80 
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 projecting 
beyond. the’ carapace is comparatively shorter 
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 
Pl. XIII, fig. 27). The last segment, however, is 
very distinctly defined, and is separated from those 
in front of it by a perceptible contraction; it is also 
far larger in size, and has evidently been 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 quite short, scarcely 
more than */s of the length of the body, and exhibit 
a somewhat fusiform shape. They are set all round 
with fine, adpressed spines, which, 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, 0) 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 compound eyes. 
The first pair of antenne (Fig. 21, a*) in appear- 
ance resemble those of the full-grown animal, but 
are comparatively larger, so that they project per- 
ceptibly over the frontal margin. They do not as 
yet seem to have developed olfactory papille, but 
on the other hand one of the apical sensory bristles 
is of considerable length. 
The second pair of antenne (fig. 21, a*) of 
which there are left only slight rudiments in the 
fullgrown 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, jerky manner. Each antenna is com- 
posed of a strong cylindrical scape, divided at the 
base into several joints, and carrying at its extre- 
mity 2 very unequally 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. Each joint bears at its extremity a long, 
densely-ciliated natatory bristle. The inner ramus 
is very small, scarcely more than '/s of the length 
of the scape, is bi-articulated, and furnished at the 
