steerke, bagudrettede dorsale Torne. De sammen- 
satte Oine har tiltaget i Storrelse, og deres Syns- 
elementer er nu noksaa tydelige. Umiddelbart neden- 
for dem ligger det enkle Wie, som har bibeholdt sit 
Udseende temmelig uforandret, Af de 2 Lappe, 
hvori hos sidste Larvestadium enhver af de blind- 
sekformige Udvidninger af Tarmen var delt, viser 
den dorsale allerede en Antydning til en yderligere 
Klovning. Ungen svommer om i Vandet paa en 
fra samme hos Larverne meget forskjellig Maade, 
idet Beveegelsen nu ikke lengere er stodvis, men 
mere har Characteren af et ganske jevnt Lob, be- 
virket ved hastigt paa hinanden folgende Slag af 
Aarernes ydre Parti. Dyret vender herunder snart 
Ryg- snart Bugside opad og gjor ofte kredsformige 
Volter i Vandet. 
Paa Tab. XIV er afbildet fra venste Side 2 
umiddelbart folgende Stadier (Fig. 4 og 5), hvoraf 
vil sees, at Skallen hurtigt voxer i Storrelse, saa 
at den tilsidst er tilstrekkelig rummelig til at Le- 
gemet fuldstendigt kan trekkes ind isamme. Skal- 
lens Form er imidlertid temmelig uforandret, skjondt 
maaske noget mere oval end i Iste Stadium, og der 
er fremdeles ingen concentriske Linier at se paa 
Valvlerne. Hovedet er nu ved en tydelig dorsal 
Indbugtning sondret fra Nakkesegmentet, og den 
umiddelbart foran Indbugtningen liggende Del af 
dets dorsale Flade begynder at heve sig i Veiret 
for at danne det for det voxne Dyr saa characteri- 
stiske Fastheftningsorgan, hvilket dog endnu lenge 
udgaar fra Hovedet med en forholdsvis bred Basis. 
Pandedelen begynder lidt efter lidt at antage den 
for det voxne Dyr characteristiske koniske Form, 
og under den sees allerede en temmelig dyb Ind- 
bugtning, hvorved den sondres fra det nu triangu- 
lert fremspringende Rostrum. iste Par Folere be- 
gynder at forlenge sig og antage en smalt kolle- 
dannet Form, men er endnu hos det sidste af de 
her omhandlede 2 Stadier (Fig. 5) simple, uden late- 
rale Lappe. Aarerne, hvis basale Del nu altid er 
fortilstrakt, forandrer sig ligeledes gradvis, an- 
tagende mere og mere den for det voxne Dyr cha- 
racteristiske Bygning, idet Grenene forlenger sig 
og afsnores i et storre Antal Led. Antallet af de 
paa dem festede Svommeborster og Pigge er dog 
endnu meget ringe sammenlignet med samme hos 
det voxne Dyr. Kindbakkerne har tabt den sidste 
Rest af Mandibularfodderne og er nu, saavel hvad 
Form som Bevebning angaar, fuldkommen overens- 
stemmende med samme hos fuldt udviklede Individer. 
Branchialfoddernes Tal tiltager gradvis, idet der 
successivt bagtil danner sig nye Anleg, efterat de 
foranliggende er bleven functionsmessigt udviklede. 
Deres Tal er paa det Fig. 4 afbildede Stadium 9, 
108 
caudal lamine. Above the caudal sete moreover, 
there have developed a single pair of the strong, 
backward-pointing, dorsal spines occurring here in 
the full-grown animal. The compound eyes have 
increased in size, and their visual elements are now 
fairly distinct. Immediately below them lies the 
ocellus, which has maintained its appearance almost 
unchanged. Of the 2 lobes into which each of the 
cecal expansions of. the intestine was divided in 
the last larval stage, the dorsal one already shows 
signs of further cleavage. The young animal swims 
about in the water in a manner very different to 
that of the larva, the motion being no longer jerky, 
but having more the character of an even dart, 
brought about by the rapidly succeeding strokes of 
the distal part of the oars, during which the ani- 
mal turns now its dorsal, now its ventral side 
uppermost, and often makes circular turns in the 
water. 
On Pl. XIV, 2 immediately following stages 
(figs. 4 and 5) are illustrated from the left side. It 
will be seen from these that the shell is rapidly 
increasing in size, until at last it is sufficiently 
capacious to allow of the body being completely 
withdrawn into it. The form of the shell, however, 
is almost unchanged, though perhaps somewhat 
more oval than in the first stage, and there are 
still no concentric lines to be seen on the valves. 
The head is now divided from the cervical segment 
by a distinct dorsal depression, and that part of- 
its dorsal surface immediately in front of the de- 
pression, begins to be raised up in order to form 
the organ of attachment so characteristic of the 
adult animal, which still for some time issues from 
the head with a comparatively broad base. The 
frontal region begins little by little to assume the 
conical form characteristic of the full-grown animal, 
and beneath it may be already seen a rather deep 
depression, by which it is divided from the now 
triangularly projecting rostrum. The Ist pair of 
antenne begin to lengthen and assume a narrow 
clavate shape, but are still, in the latter of the 
2 stages now in question (fig. 5), simple and without 
lateral lobes. The oars, whose basal part is now 
always extended forwards, are also changing gra- 
dually, and assuming more and more the structure 
characteristic of the adult animal, the rami being 
elongated and divided into a greater number of 
joints. The number of natatory bristles and spines 
attached to them is still very small compared with 
that in the adult animal. The mandibles have lost 
the last remnants of mandibular legs, and are now, 
both as to form and equipment, exactly like those 
of the fully-developed animal. The number of 
branchial legs increases gradually, new rudiments 
being successively formed behind, as soon as those 
in front are developed sufficiently to perform their 
