Dolkhaler (Xiphosura). Det synes altsaa som om 
disse Dyr, uagtet deres Organisation idethele har 
naaet et forholdsvis meget hoit Udviklingstrin, dog 
ved Siden heraf har conserveret flere af de primitive 
Characterer, der maa antages at have udmerket de 
zldgamle Stamformer, hvorfra alle de moderne Cru- 
staceer i sidste Instans har taget sit Udspring. 
Ogsaa Udviklingen synes at stotte denne baade af 
Prof. Claus og Dr. Dohrn fremholdte Anskuelse. 
Saagodtsom hos alle Phyllopoder begynder nemlig 
den frie Udvikling med det overordentlig simple 
saakaldte Nauplius Stadium, og Larven gjennemgaar 
derpaa en Rekke af successive Omformninger, der 
lidt efter lidt forbereder Phyllopodestadiet. Det bor 
dog her bemerkes, at Dr. Packard i sit fortjenst- 
fulde Veerk over Nordamerika’s Phyllopoder heevder 
en herfra meget forskjellig Anskuelse. Efter denne 
Naturforskers Mening er Phyllopoderne tvertimod 
af meget ny Oprindelse og fremstaaet ved en videre 
Udvikling af Cladocer-Typen. Dette kunde maaske 
til Nod lade sig hore, hvor der er Sporgsmaal om 
den ene af Phyllopodernes 3 Sectioner, de saakaldte 
Conchostraca, der ganske sikkert viser en meget ud- 
preget Affinitet til Cladocererne. Men langt van- 
skeligere bliver det at faa udledet de 2 ovrige Phyl- 
lopode-Typer fra Cladocererne. Der gives ikke en 
eneste Cladocer, der viser den fjerneste Tilnermelse 
til de for Grupperne Anostraca og Notostraca cha- 
racteristiske Eiendommeligheder, og det gaar heller 
ikke an, at aflede disse 2 Typer fra den 3die Con- 
chostraca. De 3 Phyllopodetyper staar i Virkelig- 
heden paa en Maade helt isolerede og har rimelig- 
vis et meget forskjelligt Udspring. Langt natur- 
ligere end den af Packard fremsatte Hypothese om 
Phyllopodernes Afstamning fra Cladocererne, synes 
det mig at vere at vende Sagen helt om, og altsaa 
antage, at Cladocererne er af yngre Oprindelse end 
Phyllopoderne og har udviklet sig som en Sidegren 
fra Gruppen Conchostraca. Raadsperger vi Pale- 
ontologien, vil ialfald intet Modbevis mod en saadan 
Antagelse kunne hentes herfra; tvertimod. Medens 
man nemlig endnu ikke kjender en eneste Cladocer 
i fossil Tilstand, finder man talrige fossile Skaller 
af utvivlsomme conchostrake Phyllopoder, nermest 
henhorende til Slegten Estheria, lige op til den De- 
voniske Periode; noget der jo viser, at ialfald denne 
Gruppe af Phyllopoder ikke kan vere af saa ny 
Oprindelse, som man efter Packards Hypothese synes 
at maatte antage. Nu er der forskjellige morpho- 
logiske Forhold, der gjor det hoist usandsynligt at 
antage, at Gruppen Conchostraca skulde repreesen- 
tere de wldste og oprindeligste Phyllopoder. 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 forverdenske Former af disse sidste 
Grupper, kan naturligt forklares af de herhen ho- 
37 
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 have retained several of the primitive 
characteristics which must be assumed to have 
distinguished the ancient ancestors, from which 
all the modern crustaceans have finally had their 
origin. The development also seems to support 
that view, advocated both by Prof. Claus and Dr. 
Dohrn. In almost all the ~Phyllopods the free 
development begins, namely, with the extraordi- 
narily simple so-called Nauplius stage; and the 
larva thereupon undergoes a series of successive 
transformations, which, little by little, prepare the , 
phyllopod-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 anything better, be accepted, 
when the question concerns one of the 3 sections of 
Phyllopods, the so-called Conchostraca, which quite 
certainly exhibits a very distinguished affinity to 
the 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 the characteristics 
peculiar to the groups Anostraca and Notostraca, 
and neither is it permitted for us to trace these 
2 types trom the 3rd, the Conchostraca. The 3 types 
of Phyllopods stand in reality, in a measure, quite 
isolated, and probably have a very different origin. 
Far more natural than the hypothesis of the deri- 
vation of the Phyllopods from the Cladocera, pre- 
sented by Packard, does it appear, to me, to be, to 
quite reverse the case, and consequently assume that 
the Cladocera are of later origin than the Phyllo- 
pods and have become developed, as a lateral branch, 
from the group Conchostraca. If we consult pale- 
ontology, we will, at any rate, find no testimony 
rebutting such an assumption to be obtained there- 
from; on the contrary, while we do not yet know 
of a single Cladoceran in fossil condition, we find 
numerous fossil remains of indubitable conchostracan 
Phyllopods most closely approaching to the genus 
Estheria, even up to the Devonian period; a fact 
that certainly shows that that group of Phyllopods, 
at any rate, cannot be of such late origin as we, 
according to Packard’s hypothesis, seem obliged to 
suppose. Now there are various morphological rela- 
tions that make it extremely improbable to suppose 
that the group Conchostraca represents the oldest 
