37 



Dolkiialer (Xiphosura). Det synes altsaa som om 

 disse Dyr, nagtet deres Organisation idethele bar 

 naaet et forholdsvis meget boit Udviklingstrin, dog 

 ved Siden beraf bar conserveret flere af de primitive 

 Cbaracterer, der maa antages at bave udmærket de 

 ældgamle Stamformer, bvorfra alle de moderne Cru- 

 staceer i sidste Instans bar tåget sit Udspring. 

 Ogsaa Udviklingen synes at stotte denne baade af 

 Prof Claus og Dr. Dobrn fremboldte Anskuelse. 

 Saagodtsom bos alle Pbyllopoder begynder nemlig 

 den frie Udvikling med det overordentlig simple 

 saakaldte Nau])lius Stadium, og Larven gjennemgaar 

 derpaa en Række af successive (Jmformuinger, der 

 lidt efter lidt forbereder Pb^dlopodestadiet. Det bor 

 dog ber bemærkes, at Dr. Packard i sit fortjeust- 

 fulde Værk over Nordamerika's Pbyllopuder bævder 

 en berfra meget forskjellig Anskuelse. Efter denne 

 Naturforskers Mening er Pbyllopoderue tværtimod 

 af meget ny Oprindelse og frenistaaet ved en videre 

 Udvikling af Cladocer-Tj^pen. Dette kunde maaske 

 til Nød lade sig bore, bvor der er Sporgsmaal om 

 den ene af Pbyllopodernes H Sectioner, de saakaldte 

 Concbostraca, der ganske sikkert viser en meget ud- 

 præget Affinitet til Cladocererne. Men langt van- 

 skeligere bliver det at faa udledet de 2 ovrige Pbyl- 

 lopode-Typer fra Cladocererne. Der gives ikke en 

 eneste Cladocer, der viser den fjerneste Tilnærmelse 

 til de for Grupperne Anostrac;i og Notostraca cba- 

 racteristiske Eiendommeligbeder, og det gaar heller 

 ikke an, at aflede disse 2 Typer fra den 3die Con- 

 cbostraca. De 3 Pbyllopodetyper staar i Virkelig- 

 heden paa en Maade belt isolerede og bar rimelig- 

 vis et meget forskjelligt Udspring. Langt natur- 

 ligere end den af Packard fremsatte Hypothese om 

 Pbyllopodernes Afstamning fra Cladocererne, synes 

 det mig at være at vende Sagen helt om, og altsaa 

 antage, at Cladocererne er af yngre Oprindelse end 

 Phyllopoderne og bar udviklet sig som en Sidegren 

 fra Gruppen Concbostraca. Raadsperger vi Palæ- 

 ontologien, vil ialfabl intet Modbevis mod en saadan 

 Antagelse kunne hentes berfra; tværtimod. Medens 

 man nemlig endnu ikke kjender en eneste Cladocer 

 i fossil Tilstand, finder man talrige fossile Skaller 

 af utvivlsomme concbostrake Pliyllopoder, nærmest 

 benborende til Slægten Esllierkt. lige op til den De- 

 voniske Periode; noget der jo viser, at ialfald denne 

 Gruppe af Pbyllnpoder ikke kan være af saa ny 

 Oprindelse, som man efter Packai'ds Hypothese synes 

 at maatte antage. Nu er der forskjellige morpbo- 

 logiske Forhold, der gjor det hoist usandsynligt at 

 antage, at Gruppen Concbostraca skiilde repræsen- 

 tere de ældste og oprindeligste Pbyllopoder. Vi 

 kommer ad denne Vei snarere til en stik modsat 

 Slutning, nemlig at denne Gruppe er af en betyde- 

 lig yngre Oprindelse end de 2 ovrige. At man ikke 

 kjender nogen for verdenske Former af disse sidste 

 Grupper, kan naturligt forklares af de barben bo- 



the division Notostraca, at any rate, is an unmistak- 

 able habitual resemblance with the sword-tails (Xi- 

 phosura), likewise passing far back in geological 

 times It appears therefore, as if these animals, 

 although their organisation has, upon the whole, 

 attained, relatively, a very high stage of develop- 

 ment, still bave retained several of the primitive 

 characteristics which must be assumed to have 

 distinguished the ancient ancestors, from which 

 all the modern crustaceans have finalh' bad their 

 origin. The development also seems to support 

 that view, advocated both by Prof. Claus and Dr. 

 Dobrn. In almost all the Phyllopods the free 

 development begins, namely, with the extraordi- 

 narily simple so-called Nauplius stage; and the 

 larva thereupon iTudergoes a series of successive 

 transformations, which, little by little, prepare the 

 pbyllopod-stage. It ought to be noted here, how- 

 ever, that Dr. Packard in his admirable work 

 upon the Phyllopods of North America, maintains 

 a very different view. According to the opinion 

 of that naturalist, the Phyllopods are, on the con- 

 trary, of very late origin, and produced by a further 

 development of the Cladocera-type. That might per- 

 haps, in the absence of anj^tbing better, be accepted, 

 when tbe question concerns one of the 3 sections of 

 Phyllopods, tbe so-called Concbostraca, which ijuite 

 certainly exhibits a very distinguished affinity to 

 tbe Cladocera. But far more difficult does it become, 

 to trace the 2 other phyllopod-types from the Cla- 

 docera. There is not a single Cladoceran that exhi- 

 bits the slightest approximation to tbe characteristics 

 peculiar to the groups Anostraca and Notostraca, 

 and neither is it permitted for its to trace these 

 2 types from tbe 3rd, tbe Concbostraca. Tbe 3 types 

 of Phyllopods stand in reality, in a measure, quite 

 isolated, and probabh' have a very different origin. 

 Far more natural than tbe hypothesis of tbe deri- 

 vation of the Phj'llopods from tbe Cladocera, pre- 

 sented b}' Packard, does it appear, to me, to be, to 

 quite reverse the case, and consequentlj^ assume that 

 the Cladocera are of later origin than tbe Phyllo- 

 pods and bave become developed, as a lateral branch, 

 from tbe group Concbostraca. If we consult palæ- 

 ontology, we will, at any rate, find no testimony 

 rebutting such an assumption to be obtained there- 

 from ; on tbe contrary, while we do not yet know 

 of a single Cladoceran in fossil condition, we find 

 numerous fossil remains of indubitable concbostracan 

 Phyllopods most closely approaching to tbe genus 

 Estherin, even up to the Devonian period; a fact 

 that certainly shows that that group of Phyllopods, 

 at any rate, cannot lie of such late origin as we, 

 according to Packard's hy])otbesis, seem obliged to 

 suppose. Now there are various morphological rela- 

 tions that make it extremely improbable to suppose 

 that the group (.-onchostraca represents the oldest 



