109 



jma det Fig. 5 fremstillecle 14 Par ialt. Haledelen 

 sondrer sig tydeligere fra Trimciis og bliver mere 

 omboiet. Haleklonie er nu bevægeligt articnlerede 

 ])aa Sjndsen, og Halepladerne begynder at springe 

 stærkere frem. I deres Bagkant viser sig nogle faa 

 tandformige Fremspring, ligesom de ovenfor Hale- 

 børsterne iidgaaende dorsale Torne begynder at til- 

 tage i Antal. Hvad den indre Organisation angaar, 

 skal her blot henledes Opmærksomlieden paa den 

 ganske gradvise Udvikling at det i Hovedet liggende 

 leveragtige Organ, der allerede i det sidste af de 2 

 lier omhandlede Stadier (Fig. 5) har opnaaet en 

 temmelig compliceret Bygning. Længden af Skallen 

 hos disse 2 Stadier er henholdsvis 1,10 mm. og 2,30 

 mm. Endnii foregaar der en lignende gradvis Ud- 

 vikling af alle Dele af Legemet indtil Skallen har 

 naaet en Længde af 6 — 7 mm. Da indtræder den 

 Lste Hndskiftning inden den postlarvale Tilstand, 

 og meget kort Tid efter denne er allerede Individet 

 kjonsniodent, skjønt det endnii neppe har opnaaet 

 synderlig mere end Halvparten af dets delinitive 

 Størrelse, 



Fig. 6 paa samme Planehe fremstiller et Individ 

 nogen Tid efterat denne Hndskiftning er foregaaet. 

 Som man ser, har Valvlerne nu faaet sin forste 

 Væxtstribe, der lober nogenlunde parallel med og i 

 forholdsvis kort Afstand fra Valvlernes frie Rand. 

 Dannelsen af denne Væxtstribe er ikke vanskelig 

 at forståa. Ved Hudskiftningen bliver nemlig kun 

 den indre Membran af Skallen afkastet, medens den 

 ydre chitinøse Lamelle bliver siddende igjen og sup- 

 pleres nu med en nydannet peripher Del. Denne 

 Iste Væxtstribe er altsaa intet andet end Kanterne 

 af de primære Valvler, der skarpt afgrændser sig 

 fra den efter Hudskittningen optrædende nydannede 

 Del af Valvlerne. Skallen, der nu har en Længde 

 af 8 mm. og en Høide af 6 mm., har den dorsale 

 Kant jevnt liueformig bøiet, dog langtfra saa stærkt 

 som hos fuldt irdvoxede Individer, og det forreste 

 Hjorne er, i Modsætning til hvad Tilfældet er hos 

 disse, fuldkommen ligesaa stærkt fremtrædende som 

 det bagre. Det i Skallen indesluttede Dyr er i alle 

 Henseender normalt udviklet, alene med den For- 

 skjel, at Branchialføddernes Antal er noget ringere 

 end hos fuldvoxne Exemplarer, nemlig kun 20 tyde- 

 ligt iidviklede Par, hvoraf allerede 9de til Ilte Par 

 har den ovre Lap af Exopoditen traadformigt for- 

 længet. Til Siderne af Tarmen sees nu tydeligt 

 Ovarierne med sine talrige Ægfollikler, og i deres 

 indre har allerede afsat sig det opakt hvide Secret, 

 der skal tjene til Dannelsen af Ægkapslerne. Efter 

 nogen Tids Forlob har Individet faaet sin charac- 

 teristiske Ægmasse under den dorsale Del af Skal- 

 len. Denne bæres i Regelen af Dyret til næste 

 Hixdskiftning, da den sammen med den afkastede 

 Hud bliver udstodt af Skallen bagtil. Efter Hnd- 



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 trunlc, and becomes more bent downwards. 

 The caudal claws are now movably articulated at 

 the point, and the caudal lamellæ begin to project 

 more. On their hind margin a few denticular pro- 

 minences appear, while the dorsal spines issuing 

 from above the caudal setæ, 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 toleraldy 

 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 (> 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 has 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 exiiviation, only the inner membrane of the 

 shell is cast, while the outer diitinons lamella 

 remains, and receives the addition of a newlj'-formed 

 peripheral part. This 1st 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 () 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 i^rominent 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 numljer 

 than in adult specimens, there being only 20 dis- 

 tinctly developed pairs, the 9th, 10th and Uth 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 



