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paa det Fig. 5 fremstillpde 14 Par ialt. Haledpleii 

 sondrer sig tydeligere fra Trixncus og l)liver mere 

 omboiet. Haleklorne er nu hevægeligt artimilerede 

 jiaa Sjiidseii, og Halepladerne liegyiuler at springe 

 stærkere frem. I deres Bagkant viser sig nogle faa 

 tandfnrmige Fremspring, ligesom de ovenfor Hale- 

 børsterne udgaaende dorsale Torne begynder at til- 

 tage i Antal. Hvad den indre ( (rganisation angaar, 

 skal her blot lienledes Opniærksomheden ]iaa 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 

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

 mm. Endnii foregaar der en lignende gradvis Ud- 

 vikling af alle Dele af Ijegemet indtil Skallen har 

 naaet en Længde af (3 — 7 mm. Da iiultræder den 

 Iste Hndskiftniiig inden den postlarvale Tilstand. 

 Dg meget kort Tid etter denne er allerede Individet 

 kjonsnnjdent, skjont det endnu neii])e har opnaaet 

 synderlig mere end Halvparten af dets definitive 

 Størrelse. 



Fig. (1 paa samme Planehe fremstiller et Individ 

 nogen Tid etterat denne Hndskiftning er foregaaet 

 Som man ser, har Val vierne nn faaet sin firste 

 Væxtstribe, der lober nogenlnnde parallel med og i 

 fordioldsvis kort Afstaiul fi-a Valvleriies frie Rand. 

 Dannelsen af denne Væxtstribe er ikke vanskelig 

 at forståa. Ved Hndskiftningen bliver nemlig knn 

 den indre Memln'an af Skallen afkastet, medens den 

 ydre ehitinose Lamelle bliver siddende igjen og snp- 

 pleres nn med en nydannet peripher Del. Denne 

 Iste Væxtstrilie er altsaa intet andet end Kanterne 

 af de primære Valvler, der .skarpt afgrændser sig 

 fra den efter Hndskiftningen optrædende nydannede 

 Del af Valvlerne. Skallen, der nn har en Længde 

 af 8 mm. og en Hoide af I! nnn , har den dorsale 

 Kant jevnt bueformig boiet, dog langtfra saa stærkt 

 som hos fuldt ndvoxede Individer, og det forreste 

 Hjørne 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 Branehialfoddernes Antal er noget ringere 

 end hos fuldvoxne Exemplarer, nemlig knn 20 tyde- 

 ligt ndviklede Par, hvoraf allerede 9de til lite Par 

 har den ovre Lap af Exopoditen traailformigt for- 

 længet. Til Siderne af Tarmen sees nu tydeligt 

 ( Ivarierne med sine talrige Ægfollikler, og i deres 

 indre har allerede afsat sig det o]iakt hvide Seeret, 

 der skal tjene til Dannelsen af Ægka])slerne, Efter 

 mjgen Tids Forløb har Individet faaet sin eharae- 

 teristiske Ægmasse nnder den dorsale Del af Skal- 

 len. Denne liæres i Regelen af Dyret til næ.ste 

 Hndskiftning, da den sammen med den afkastede 

 Hnd bliver ndstodt af Skallen bagtil. Efter Hud- 



functimis. In the stage shown in hg. 4, their 

 number is 9 pairs, in that in tig. 5, there are in all 

 14 pairs. The caudal part is more distinetly divided 

 from the trunk', and lieeimies more bent downwards. 

 The caudal claws ai'e now movabl.y ai'ticnlated at 

 the point, and the caudal lamellæ liegin to project 

 more. On their hind margin a few denticular jirci- 

 minences appear, while the dorsal spines issuing 

 from above the caudal seta', begin to augment in 

 numl)er. With regai'il to the internal organisatiim, 

 attention is here only drawn to the very gradual 

 develojiment of the hejiatic organ in the head, 

 whicli, in the latter of the 2 stages here under dis- 

 cus.sion (tig. 5), has already attained a tolerably 

 complicated structure. The length of the shell in 

 these 2 stages is respectively 1.10 mm. and 2.'>0 

 mm. A gradual tlevelopment of this kind still goes 

 on of all the parts of the body, until the shell has 

 attained a length of (i 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 lias scarcely attained more than half 

 its eventual size. 



Fig. () on the same ])late. 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 1st line of growth is thus 

 nothing more than the edges of the primary valves, 

 which are sharply defined against the newh^-formed 

 ])ortion of the valves appearing after the exuviation. 

 The shell, which now has a length of 8 mm. and a 

 height of r> mm., has its dorsal edge evenly curved, 

 though not nearl\' 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 emdosed in the shell is in every 

 respect normally developed, with the one exception 

 that the branchial legs are rather fewer in mrmber 

 than in adult specimens, there being only 20 dis- 

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

 which already have the filiform elongation of the 

 exopodite. The ovaries with their numerous egg- 

 follicles are now distinctlj' visible at the sides of 

 the intestine, and the opaque white secretion to be 

 employed in the formation of the egg-capsules has 

 already Ijeen dejtosited 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 



