paa det Fig. 5 fremstillede 14 Par ialt. 
sondrer sig tydeligere fra Truncus og bliver mere 
omboiet. Haleklorne er nu bevegeligt articulerede 
paa Spidsen, og Halepladerne begynder at springe 
steerkere frem. I deres Bagkant viser sig nogle faa 
tandformige Fremspring, ligesom de ovenfor Hale- 
borsterne udgaaende dorsale Torne begynder at til- 
tage i Antal. Hvad den indre Organisation angaar, 
skal her blot henledes Opmerksomheden paa den 
ganske gradvise Udvikling af det i Hovedet liggende 
leveragtige Organ, der allerede i det sidste af de 2 
her omhandlede Stadier (Fig. 5) har opnaaet en 
temmelig compliceret Bygning. Leengden af Skallen 
hos disse 2 Stadier er henholdsvis 1,10 mm. og 2,30 
mm. Endnu foregaar der en lignende gradvis Ud- 
vikling af alle Dele af Legemet indtil Skallen har 
naaet en Lengde af 6—7 mm. Da indtreder den 
Iste Hudskiftning inden den postlarvale Tilstand, 
og meget kort Tid efter denne er allerede Individet 
kjonsmodent, skjont det endnu neppe har opnaaet 
synderlig mere end Halvparten af dets definitive 
Storrelse. 
Fig. 6 paa samme Planche fremstiller et Individ 
nogen Tid efterat denne Hudskiftning er foregaaet. 
Som man ser, har Valvlerne nu faaet sin forste 
Veextstribe, der lober nogenlunde parallel med og i 
forholdsvis kort Afstand fra Valvlernes frie Rand. 
Dannelsen af denne Veextstribe er ikke vanskelig 
at forstaa. Ved Hudskiftningen bliver nemlig kun 
den indre Membran af Skallen afkastet, medens den 
ydre chitinose Lamelle bliver siddende igjen og sup- 
pleres nu med en nydannet peripher Del. Denne 
lste Veextstribe er altsaa intet andet end Kanterne 
af de primere Valvler, der skarpt afgrendser sig 
fra den efter Hudskiftningen optreedende nydannede 
Del af Valvlerne. Skallen, der nu har en Lengde 
af 8 mm. og en Hoide af 6 mm., har den dorsale 
Kant jevnt bueformig boiet, dog langtfra saa sterkt 
som hos fuldt udvoxede Individer, og det forreste 
Hjorne er, i Modsetning til hvad Tilfeeldet er hos 
disse, fuldkommen ligesaa sterkt fremtreedende som 
det bagre. Det i Skallen indesluttede Dyr er i alle 
Henseender normalt udviklet, alene med den For- 
skjel, at Branchialfoddernes Antal er noget ringere 
end hos fuldvoxne Exemplarer, nemlig kun 20 tyde- 
ligt udviklede Par, hvoraf allerede 9de til 11te Par 
har den ovre Lap af Exopoditen traadformigt for- 
lenget. Til Siderne af Tarmen sees nu tydeligt 
Ovarierne med sine talrige Agfollikler, og i deres 
indre har allerede afsat sig det opakt hvide Secret, 
der skal tjene til Dannelsen af Mgkapslerne. Efter 
nogen Tids Forlob har Individet faaet sin charac- 
teristiske Aigmasse under den dorsale Del af Skal- 
len. Denne beres i Regelen af Dyret til neste 
Hudskiftning, da den sammen med den afkastede 
Hud bliver udstodt af Skallen bagtil. Efter Hud- 
109 
Haledelen | functions. 
In the stage shown in fig. 4, their 
number is 9 pairs, in that in fig. 5, there are in all 
14 pairs. The caudal part is more distinctly divided 
from the trunk, and becomes more bent downwards. 
The caudal claws are now movably articulated at 
the point, and the caudal lamelle begin to project 
more. On their hind margin a few denticular pro- 
minences appear, while the dorsal spines issuing 
from above the caudal sete, begin to augment in 
number. With regard to the internal organisation, 
attention is here only drawn to the very gradual 
development of the hepatic organ in the head, 
which, in the latter of the 2 stages here under dis- 
cussion (fig. 5), has already attained a tolerably 
complicated structure. The length of the shell in 
these 2 stages is respectively 1.10 mm. and 2.30 
mm. A gradual development of this kind still goes 
on of all the parts of the body, until the shell has 
attained a length of 6 or 7 mm. Then occurs the 
1st exuviation in the post-larval condition, and very 
shortly after this, the animal is sexually mature, 
although it kas scarcely attained more than half 
its eventual size. 
Fig. 6 on the same plate, represents an animal 
some time after this exuviation has taken place. 
It will be seen that the valves have now acquired 
their first line of growth, which runs almost parallel 
with, and at a comparatively short distance from 
the free edge of the valves. The formation of this 
line of growth is not difficult to understand, for in 
the exuviation, only the inner membrane of the 
shell is cast, while the outer chitinous lamella 
remains, and receives the addition of a newly-formed 
peripheral part. This Ist line of growth is thus 
nothing more than the edges of the primary valves, 
which are sharply defined against the newly-formed 
portion of the valves appearing after the exuviation. 
The shell, which now has a length of 8 mm. and a 
height of 6 mm., has its dorsal edge evenly curved, 
though not nearly so much as in fully developed 
specimens; and the foremost corner, unlike that in 
‘adult animals, is fully as prominent as the hind 
one. The animal enclosed in the shell is in every 
respect normally developed, with the one exception 
that the branchial legs are rather fewer in number 
than in adult specimens, there being only 20 dis- 
tinctly developed pairs, the 9th, 10th and 11th of 
which already have the filiform elongation of the 
exopodite. The ovaries with their numerous egg- 
follicles are now distinctly visible at the sides of 
the intestine, and the opaque white secretion to be 
employed in the formation of the egg-capsules has 
already been deposited inside them. After some 
time has elapsed, the animal has its characteristic 
mass of eggs under the dorsal part of the shell. 
This is generally carried by the animal until the 
next exuviation, when it is cast, together with the 
