kommen typiske Branchiopoder vil vi finde, at Lem- | 
‘4 . ‘ : . : | 
merne, ved Siden af sin Function som Respirations- | 
organer, altid er af vesentlig Betydning for Til- 
veiebringelsen af Foden, idet de ved sine rythmiske 
Bevegelser frembringer en continuerlig Stremning 
af Vandet ind mod Munden, hvorved de Smaa- 
partikler, hvoraf Dyret lever, bringes indenfor Mund- 
delenes Omraade. I ethvert Fald maa den oven- 
omtalte eiendommelige Modification af Lemmerne, 
hvortil vi egentlig ikke har noget tilsvarende hos 
andre Crustaceer, .betragtes som den for de her om- 
handlede Dyr vigtigste og mest udpregede Cha- 
racter. ' 
Branchiopoderne indtager i flere Henseender en 
central Stilling inden Crustaceernes Classe, og Prof. 
Claus har endog fremsat den Hypothese, at alle 
nulevende Crustaceer i sidste Instans nedstammer 
fra en phyllopodeagtig Dyreform (Protophyllopod). 
Skjondt denne Hypothese af andre Zoologer (Packard) 
har veret bestridt, er der dog al Grund til at an- 
tage, at disse Dyr har conserveret adskillige Cha- 
racterer/ der efter al Sandsynlighed er i hoi Grad 
primitive og maaske endog skriver sig fra de eldste 
paa vor Klode optreedende Arthropoder. Allerede 
det i hai Grad varierende og ofte excessivt foragede 
Antal Kropssegmenter, samt disses ialmindelighed 
mindre skarpt udpreegede Gruppering til distincte 
Kropsafsnit, synes at vise, at vi her har at gjore 
med Former af en kun lidet udarbeidet Character, 
hos hvem endnu ikke det for Nutidens Crustaceer 
typiske Forhold rigtigt har festnet sig; og hvad 
Lemmernes Bygning angaar, saa er vel alle enige i 
at de, ialfald hos de typiske Branchiopoder, repre- 
senterer et mere primitivt Standpunkt end hos nogen 
af de ovrige Crustacegrupper. Ogsaa hvad den indre 
Organisation angaar, findes hos de herhen horende 
Former kun lidet fixerede Forhold, men derimod en 
Mangfoldighed af Modificationer i Bygningen af snart 
sagt alle Organer, hvad der ligeledes giver denne 
Crustacegruppe et ganske eiendommeligt Preeg lige- 
overfor de ovrige Ordener. Endelig vil vi i disse 
Dyrs Levevis, Forplantning og Udvikling stede paa 
baade characteriske Forskjelligheder mellem de for- 
skjellige Former og tildels ogsaa hoist eiendomme- 
lige, fra samme hos andre Crustaceer afvigende For- 
hold. Et neiere Studium af denne Crustacegruppe 
vil derfor ogsaa veere af serlig Interesse, saavel i 
phylogenetisk som biologisk Henseende og vil pas- 
sende kunne tjene som Udgangspunkt ved Bearbei- 
delsen af den her omhandlede Dyreclasse. 
may also, to some extent, be demonstrated in forms 
with otherwise normally developed branchial-legs 
e. g. Apus. Also in perfectly typical Branchiopods 
we may observe that the appendages, besides their 
function as respiratory organs, are always of mate- 
rial importance in the procuring of the nutriment, 
as they by their rhythmical movement produce a 
continuous current of the water in towards the 
mouth, by which the minute particles upon which 
the animal exists are brought within the range of 
the oral parts. At any rate, the above mentioned 
peculiar modification of the appendages, to which 
we meet with nothing really correspondent in other 
Crustaceans, must be considered to be the most 
important and prominent characteristic of the ani- 
mals here spoken of. 
The Branchiopods occupy, in several respects, a 
central position in the class of the Crustaceans, and 
_ Prof. Claus has even proposed the hypothesis, that 
all the now-existent Crustaceans may descend, in 
the final instance, from a phyllopodous animal-form 
(Protophyllopod). Although that hypothesis has been 
rejected by other zoologists (Packard), there is still 
every reason to assume that those animals have 
retained several characteristics which are, in all 
probability in a high degree primitive, and perhaps 
even emanate from the-oldest Arthropods that 
have appeared on our Earth. The extremely vari- 
able and frequently excessively increased number 
of body-segments, as well as in general their 
less distinctly prominent grouping into distinct’ 
sections, at once appears to point to the circum- 
stance that we have here to do with forms of only 
vaguely developed character, in which the typical fea- 
tures characteristic of the modernly existent Crusta- 
ceans, have not yet become permanently established: 
and as regards the structure of the appendages all 
unite, we believe, in the opinion that it, at any rate 
in the typical Branchiopods, represents a more pri- 
mitive condition than in, any of the other groups 
of Crustaceans. Also in regard to the internal or- 
ganization there is found, in the forms belonging 
to this order, only little of permanent features but, 
on the other hand, a multitude of modifications in 
the structure of, it may be said, all the organs, 
a circumstance that also imparts to this group of 
Crustaceans a quite peculiar imprint compared with 
the other orders. Finally we meet in these ani- 
mals’ mode of life, propagation and development, 
both characteristic differences between the various 
forms and partly, also, highly peculiar features 
differing from those in other Crustaceans. <A closer 
study of this group of Crustaceans will, therefore, 
prove of special interest, both in phylogenetic 
and biological respects, and will serve as a suitable 
point of departure in the treatment of the animal- 
class here spoken of. : 
