100 



fra buede Sideribber vxdgaar til den modstaaende 

 TJdvidning, livilken sidste ender med en tilskjærpet 

 Kant og viser en fint cellulos Structur (se Fig. 23). 

 Ved hvilke mekaniske Midler denne eiendommelige 

 Form af Ægkapselen, der er noiagtig ligedan hos 

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

 Rimeligvis spiller herved den skrueformige Dreining 

 af Ovarialtuberne en væsentlig Rolle. Ægma.ssen 

 bliver med visse Mellemrnm, rimeligvis i Forbindelse 

 med Hudskiftningsakten, iidstodt af Skallen, og fal- 

 der derpaa tilbiinds, hvor den indleires i Mndret. 

 Imidlertid har Ovarierne prodnceret et nyt Sæt Æg, 

 .som snart samler sig til en ny Ægmasse ixnder 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 udklækkes dog i 

 Regelen aldrig samme Aar, som de er lagte, men 

 er alle bestemte til at overvintre; ja der er (xrund 

 til at antage, at de i mange Tilfælde kan henligge 

 i en hvilende Tilstand gjennem meget lange Tids- 

 rum, tildels fuldstændig indtørrede, for de ud- 

 klækkes. 



Udvikling. — Om Udviklingen af denne Phyllo- 

 pode har den franske Naturforsker LerebouUet i 

 Aaret 1866 *) leveret en meget ndførlig, af Afbild- 

 ninger ledsaget Fremstilling, hvortil senere Forskere 

 altid har henholdt sig, uden at der, saavidt mig 

 bekjendt, er anstillet fornyede Undersogelser over 

 denne Side af nærværende Forms Biologi. Ogsaa 

 Kjonsorganernes Bygning er af samme Forsker 

 meget udforligt omtalt i samme Afhandling, men 

 hans Fremstilling er her i flere væsentlige Punkter 

 urigtig og misvisende. Da jeg har havt en sjelden 

 god Anledning til at studere denne Forms Udvik- 

 ling og tror i flere væsentlige Punktei' at kunne 

 .supplere og berigtige den af Lereboiillet givne Frem- 

 stilling, skal jeg i det følgende forsøge noget ud- 

 førligere at beskrive samme. 



Udvildingen kan passende inddeles i 2 Perioder, 

 den larvale og postlarvale, begge vel markerede fra 

 hinanden. Den forste Periode er tilendebragt i 

 meget kort Tid, ialmindelighed i Løbet af nogle faa 

 Dage, hvorimod der til den anden Periode udkræves 

 mindst en hel Maaned. 



Larveudviklingen. — Larven kommer til Ver- 

 den i en yderst ufuldkommen Tilstand, som en saa- 

 kaldt Nauplius, uden at vise nogensomhelst 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 bagerste 



') Annales des Sciences naturelles, Zoologie, ome Serie, T. V. 



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

 perpendicular to one another. Along one of these 

 expansions runs a distinctly thickened rib, fi'om 

 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 peculiar 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 ovarial 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 thereiipon 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 prodi^ce 

 an enormous number of eggs. These, however, as a 

 rule, are never hatched in the same 3'ear that they 

 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 quiescence for 

 very long periods of time, sometimes completely 

 dried u]>, before they are hatched. 



Development. — The French naturalist Lere- 

 bouUet, in the year 1866'), published a very detailed 

 account of the development of this Phjdlopod, 

 accompanied by illustrations; and more x'ecent 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 

 laeen 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- 

 siially good ojiportunity of studying the develop- 

 ment of this form, and believe that in several 

 important jioints I can sujiplement and correct the 

 account given by Lereboullet, I will here endeavour 

 to describe it somewhat more fully. 



The development ma^^ be suitably divided into 

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

 marked. The first period is broirght to a conclusion 

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

 whereas at least a month is required 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 length 

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

 equal size, defined by a slight median contraction. 

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



') Annales des Sciences naturelles, Zoologie, ome Serie, T. V. 



