100 



fra buede Sideribber udgaar til den modstaaende 

 Udvidning, hvilken sidste ender med en tilskjærpet 

 Kant og viser en lint eellulos Struetur (se Fig. 23). 

 Ved hvilke mekani.-^ke Midler denne eiendoninielige 

 Form af Ægkap.selen, der er noiagtig ligedan hos 

 alle Æg, tilveiebringes, er ikke saa godt at sige. 

 Rimeligvis spiller herved den skrneformige Dreining 

 af ()varialtuberne en væsentlig Rolle. Ægma.ssen 

 liliver med visse Mellemrum, rimeligvis i Forlnndelse 

 med Hndskiftningsakten, ndstodt af Skallen, og fal- 

 der derpaa tilbunds, hvor den indleires i Mudret. 

 Imidlertid har Ovarierne produceret et nyt Sæt Æg, 

 som snart samler sig til en ny Ægmasse under den 

 dorsale Del af Skallen. Paa denne Maade kan et 

 og samme Individ i Løbet af nogle Uger producere 

 et enormt Antal af Æg. Disse ndklækkes dog i 

 Regelen aldrig samme Aar, som de er lagte, men 

 er alle l^estemte til at overvintre; ja der er (Irund 

 til at antage, at de i mange Tilfælde kan henligge 

 i en hvilende Tilstand gjennem meget lange Tids- 

 rum, tildels fuldstændig indtorrede, for de nd- 

 klækkes. 



Udvikling. — Om Ud viklingen af denne Phyllo- 

 ])ode har den franske Naturforsker Lerebonllet i 

 Aaret 1866 ') leveret en meget udførlig, af Afbild- 

 ninger ledsaget Fremstilling, hvortil senere Forskere 

 altid har henholdt sig, uden at der, saavidt mig 

 bek j endt, er anstillet fornyede Undersogelser over 

 denne Side af nærværende Forms Biologi. Ogsaa 

 Kjønsorganernes Bygning er af samme Forsker 

 meget udforligt omtalt i samme Afhandling, men 

 hans Fremstilling er her i flere væsentHge Punkter 

 nrigtig og misvisende. Da jeg har havt en sjelden 

 god Anledning til at studere denne Forms Udvik- 

 ling og tror i flere væsentlige Punkter at kunne 

 supplere og berigtige den af Lerebonllet givne Frem- 

 stilling, skal jeg i det følgende forsoge iioget ud- 

 forligere at beskrive samme. 



Udviklingen kan passende inddeles i 2 Perioder, 

 den larvale og postlarvale, begge vel markerede fra 

 hinanden. Den første Periode er tilendebragt i 

 meget kort Tid, ialmindelighed i Løbet af nogle faa 

 Dage, hvorimod der til den anden Periode udkræves 

 niindst en hel JEaaned. 



Larveudviklingen. — Larven kommer til Ver- 

 den i en j-derst ufuldkommen Tilstand, som en saa- 

 kaldt Nauplius, uden at vise Jiogensomhelst Lighed 

 med det voxne Dyr. Legemet har i dette Iste Sta- 

 dium (Tab. XVIl', Fig. 1) kun en Længde af 0,25 

 mm. og bestaar af 2 ved en svag median Indknib- 

 ning sondrede Afsnit af omtrent lige Størrelse. Det 

 forreste Afsnit repræsenterer Hovedet, det bager.ste 



') Annales des bciences naturelles, Zoologie, orae Serie, T. V. 



figs. 20, 21, 22) with 2 wing-like expansions placed 

 jierpendicular to one another. Along one of these 

 expansions runs a distinctly thickened rib, from 

 which curved lateral ribs run to the opposite expan- 

 sion, this last ending in a sharp edge, and exhibiting 

 a finely cellular structure (see fig. 23). By what 

 mechanical means this 2)ecviliar form of egg-capsule, 

 which is exactly similar in all the ova, is brought 

 about, it is not easy to say. Probably the screw- 

 like twist of the oA'arial tubes has much to do with 

 it. The egg-mass, at certain intervals, probably 

 connected with the process of exuviation, is thrust 

 out of the shell, and thereupon sinks to the 

 bottom, where it is imbedded in the mud. In the 

 meantime the ovaries have produced a new set of 

 ova, which soon collect into a new egg-mass beneath 

 the dorsal part of the shell. In this way, one 

 animal, in the course of a few weeks, can produce 

 an enormous nundier of eggs. These, liowever, as a 

 rule, are never hatched in the same year that thej' 

 are laid, but are all designed to stand a winter; 

 indeed, there is reason to suppose that in many 

 cases they may lie in a state of qi^iescence for 

 vei'y long periods of time, sometimes completely' 

 dried u]), before they are hatched. 



Development. — The French naturalist Lere- 

 bonllet, in the year 1866 \"), pul)lislied a very detailed 

 account of the development of this Phyllopod, 

 accompanied by illustrations; and more recent na- 

 turalists have always referred to this, without, as 

 far as I am aware, any fresh investigations on this 

 point in the biology of the present form having 

 been instituted. The structure of the sexual organs 

 is also very fully described in the above treatise, 

 but here his description, in many essential points is 

 incorrect and misleading. As I have had an unu- 

 sually good opportunity of studying the develop- 

 ment of this form, and believe that in several 

 important points I can sujiplement and correct the 

 account given by Lerebonllet, I will here endeavour 

 to describe it somewhat more fully. 



The development may be suitably divided into 

 2 periods, the larval and the post-larval, both well- 

 marked. The first period is brouglit to a conclusion 

 in a very short time, generally in a few days, 

 whereas at least a month is reqxiired for the second. 



Larval Development. — The larva is brought 

 into the world in an exceedingly imperfect condition, 

 as a so-called nauplius, without exhibiting any 

 resemblance whatever to the adult animal. The 

 body in this 1st stage (PI. XVII, fig. 1) has a lengtli 

 of only 0.25 mm., and consists of 2 sections of about 

 e(|nal size, defined by a slight median conti'action. 

 The front section represents the head, the hind one, the 



') Annaies des Sciences naturelles, Zoologie, .5me Serie, T. V. 



