kommeu typiske Branchiopoder vil vi fiude, at Lem- 

 merne, ved Siden af sin Function som Respirations- 

 organer, altid er af væsentlig Betydning for Til- 

 veiebringelsen af Foden, idet de ved sine rythmiske 

 Bevægelser frembringer en rontinuerlig Strømning 

 af Våndet ind mod Mnnden, hvorved de Smaa- 

 partikler, hvoraf Dyret lever, bringes iudeufor Mund- 

 delenes Omraade. I ethvert Fald maa den oven- 

 omtalte eiendommelige Modification af Lemmerne, 

 hvortil vi egentlig ikke har uoget tilsvarende hos 

 andre Crnstaceer, betragtes som den for de her om- 

 handlede Dyr vigtigste og mest udprægede Cha- 

 racter. 



Branchiopoderne indtager i flere Henseender en 

 central Stilling inden Crustaceernes Classe, og Prof. 

 Claus har endog fremsat den Hypothese, at alle 

 nulevende Crnstaceer i sidste Instans nedstammer 

 fra en phyllopodeagtig D\^reform (Protophyllopod). 

 Skjondt denne Hj-pothese af andre Zoologer (Packard) 

 har været bestindt, er der dog al Grund til at an- 

 tage, at disse Dj^r har conserveret adskillige Cha- 

 racterer, der efter al Sandsynlighed er i hoi Grad 

 primitive og maaske endog skriver sig fra de ældste 

 paa vor Klode optrædende Arthropoder. Allerede 

 det i hoi Grad varierende og ofte excessivt forøgede 

 Antal Kropssegmenter, samt disses ialmindelighed 

 mindre skarpt udprægede Gruppering til distincte 

 Kropsafsnit, synes at vise, at vi her har at gjore 

 med Former af en kun lidet udarbeidet Character, 

 hos hvem eudnu ikke det for Nutidens Crustaceer 

 typiske Forhold rigtigt har fæstnet sig; og hvad 

 Lemmernes B3'gning angaar, saa er vel alle enige i 

 at de, ialfald hos de tj'piske Branchiopoder, repræ- 

 senterer et mere primitivt Standpunkt end hos nogen 

 af de ovrige Crustacegrupper. Ogsaa hvad den indre 

 Organisation angaar, findes hos de lierhen horende 

 Former kiin lidet fixerede Forhold, men derimod en 

 Mangfoldighed af Modificationer i Bj'gningen af snart 

 sagt alle Organer, hvad der ligeledes giver denne 

 Crustacegruppe et ganske eiendommeligt Præg lige- 

 overfor de øvrige Ordener. Endelig vil vi i disse 

 Dyrs Levevis, Forplantning og Udvikling stode paa 

 baade characteriske Forskjelligheder mellem de for- 

 skjellige Former og tildels ogsaa hoist eiendomme- 

 lige, fra samme hos andre Crustaceer afvigende For- 

 hold. Et nøiere Studium af denne Crustacegruppe 

 vil derfor ogsaa være af særlig Interesse, saavel i 

 phylogenetisk som biologisk Henseende og vil pas- 

 sende kunne tjene som Udgangspiinkt ved Bearbei- 

 delsen af den her omhandlede Dyrclasse. 



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 bj- 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 reallj' correspondent in other 

 Crustaceans, must be considered to be the most 

 important aiid prominent characteristic of the ani- 

 malshere spoken of. 



f^ The Branchiopods occup}-, in several respects, a 

 central position in the class of the Crustaceans, and 

 Prof. Claus has even proposed the hj-pothesis, that 

 all the now-existent Crustaceans may descend, in 

 the final instance, from a phyllopodoirs animal-form 

 (Protophyllopod). Although that hypothesis has been 

 rejected b^- other zoologists (Packard), there is still 

 every reason to assume that those animals have 

 retained several characteristics which are, in all 

 probabilitj- in a high degree primitive, and perhaps 

 even emanate from the oldest Arthropods that 

 have appeared on our Earth. The extremely vari- 

 able and frei|uentl3^ 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 j-et 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 t3qiical Branchiopods, represents a more pri- 

 mitive condition than in anj- of the other groups 

 of Crustaceans. Also in regard to the internal or- 

 ganization there is found, in the form.s belonging 

 to this order, only little of permanent features but, 

 on the other hand, a multitirde of modifications in 

 the structure of, it maj' 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 ^ifi^erences between the various 

 forms and parth-, also, highly peculiar features 

 diff'ering 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. 



f 



