36 



de ogsaa her paa samme Maade. Forskjellen er 

 altsaa, at her alle bag Munddelene folgende Lemmer 

 er ægte Braiichialfødder, medens dette hos Phyllo- 

 cariderne kun er Tilfældet med en Del af dem. 

 I Følernes Bygning er der saa stor Forskjel hos de 

 forskjellige Former, at intet andet bestemt fælles 

 Charactertræk kan anføres end, at det Iste Par ude- 

 Inkkende er sensitive og derfor af en meget tander 

 Structur. Ogsaa Øinenes Bygning er meget forskjel- 

 lig, idet de snart er stilkede som hos Phyllocariderne, 

 snart sessile, snart sammensmeltede til et enkelt i 

 det indre af Hovedet, beliggende Organ. Charaete- 

 ristisk ligeoverfor Phyllocariderne er Tilstedeværel- 

 .sen af et mediant Enkeltoie (ocellus). Angaaende 

 Munddelenes Structur, kan fremhæves Mangelen af 

 Palper paa Kindbakkerne, og den forholdsvis simple 

 Bygning af de 2 Par Kjæver. 



De hidtil bekjendte Phyllopoder vil passende 

 kunne fordeles paa 3 større Afdelinger, for hvilke 

 jeg allerede i 1867 ') har foreslaaet følgende Benæv- 

 nelser: Anostraca, Notostraca og Conchostraca. For- 

 skjellen mellem disse Afdelinger er saa stor og gjen- 

 uemgribende, at de ikke, som af de fleste Forskere 

 gjort, kau opfattes som blotte Familier, men ube- 

 tinget bør tillægges en langt høiere systematisk 

 Værdi (Tribus eller Sectioner). Til enhver af disse 

 Grupper hører et meget begrændset Antal af Slæg- 

 ter, som delvis lader sig fordele paa flere Familier. 



De herhen hørende Slægttypers Faatallighed 

 og i Regelen overordentlig skarpt udprægede For- 

 skjel, i Forbindelse med deres sporadiske Forekomst 

 paa vidt adskilte Localiteter, synes at tyde hen paa, 

 at vi i Phj'llopoderne har de sidste divergerende 

 Grrene af en uddøende Dyrgruppe, som rimeligvis, 

 at dømme efter flere palæontologiske Fund, har været 

 langt rigere repræsenteret i tidligere Jordperioder. 

 Ogsaa af disse Dyrs Organisation og Udvikling synes 

 man at være berettiget til at slutte, at de maa være 

 af meget gammel Oprindelse. Det yderlig variable 

 Antal af Kropssegmenter og af Lemmer, disse sid- 

 stes uniforme Bygning, den oftest kun lidet skarpt 

 udprægede Sondring af Legemet i tydeligt begrænd- 

 sede Kropsafsnit, alt dette er Characterer, der aaben- 

 bart heupeger paa primitive Tilstande, hvori endnu 

 ikke de hos de moderne Crustacegrupper gjældende 

 Forhold rigtigt har fixeret sig. Phyllopoderne min- 

 der i denne Henseende ikke saa lidet om de æld- 

 gamle Trilobiter, ligesom der ialfald hos Afdelingen 

 Notostraca er en umiskj en delig habituel Lighed med 

 de ligeledes langt op i den geologiske Tid gaaende 



') G. O. Sårs, Histoire naturelle des Crustacés d'eau douce 

 de Norvége, I. 



respiratory, they are also named here in the same 

 manner. The difPerence, therefore, is, that here all 

 the appendages placed behind the oral parts are 

 real branchial feet, while in the Phyllocarida that 

 is only the case with a part of them. In the 

 structure of the antennæ there is such a great differ- 

 ence in the various forms, that no other certain 

 characteristic feature in common can be given, than 

 that the 1st pair are exclusively sensitory and there- 

 fore of a very delicate structure. The structure of 

 the eyes also is very different, as they are some- 

 times pedunculated, as in the Phyllocarida, sometimes 

 sessile, sometimes coalescent to a single-organ situ- 

 ated in the interior of the head. The presence of 

 a single median eye (ocellus) is a characteristic 

 feature in contrast with the Phyllocarida. Re- 

 garding the structure of the oral parts may be 

 mentioned, the absence of palpi on the mandibles, 

 and the relatively simple structure of the 2 pairs 

 of maxiliæ. 



The Phyllopods hitherto known may suitably be 

 assigned to 3 large divisions, for which the author, as 

 early as 1867^), proposed the following designations: 

 Anostraca, Notostraca and Conchostraca. The differ- 

 ence between those divisions is throughout, so great, 

 that they cannot be regarded as families only, as 

 has been done by most writers, but ought, evid- 

 ently, to be assigned a far higher systematic value 

 (Tribus or Sections). To each of these groups 

 there pertain a very limited number of genera, 

 which to some extent may be referred to several 

 families. 



The paiicity in number of the generic types 

 . pertaining hereto, and the, as a rule, extraordinarily 

 sharply distinguished difference, in connection with 

 their sporadic occurrence in widely separated loca- 

 lities, seems to give an indication that in the Phyllo- 

 pods we have the last diverging branches of a van- 

 ishing animal group, which, probably, judging by 

 several palæontological discoveries, has been far 

 more abundantly represented in earlier periods of our 

 earth's history. From the organisation and develop- 

 ment, also, of these animals, it seems as if we were 

 warranted in conch^ding that they must be of very 

 old origin. The extremely variable number of body 

 segments and of appendages; the uniform structure 

 of the last-named; the usuallj' only little sharply 

 distinguished separation of the body in distinctly 

 defined divisions, are all charactex'istics that evid- 

 ently' point to primitive conditions, in which the 

 regulating relations of the modern groups of cru- 

 staceans had not yet been thoroughly consolidated. 

 The Phyllopods remind us in that respect, not so 

 little of the ancient Trilobites, while, also, there, in 



') G. O. Sars, Histoire naturelle des Crustacés d'eau douce 

 de Norvége, I. 



