Classification of the Crustacea, 467 



widely distributed, but also for the view that the rest of the 

 Crustacea at present in existence are referable to the three 

 types in question. In the special application of this conclusion 

 to the Brancht'pus-type^ I derive from the fact of the pre- 

 servation of this type and of the high development of that 

 of the Malacostraca a further proof of the theory that the 

 special points of agreement, albeit only small, between the 

 two types may be turned to account in the sense of establishing 

 a closer affinity, and that consequently the Malacostraca are 

 referable to the J3ranchipus-iype. 



So far as is possible I have endeavoured to establish the 

 view cherished by myself, that the Ostracoda and Cladocera 

 admit of being traced back to the Esther ia-ij^Q of the Euphyl- 

 lopoda, the Copepoda and Cirripedia to that of Apus, and the 

 Malacostraca to that of Branchipus, and that the existing 

 Crustacea are to be derived from three ancestral forms corre- 

 sponding to these types. The following genealogy (p. 468), 

 which, moreover, essentially agrees with that set up by Clans, 

 repeats this conception in tabular form. 



From this genealogical tree it is evident that the Brancliipus- 

 series in ancient times gave origin to a great Crustacean 

 group, that of the Malacostraca ; that to the Apus-s,Qx\Qa, 

 is likewise to be traced a great group, comprising the 

 Copepoda and Cirripedia ; and that, lastly, the Estheria- 

 series in ancient times also gave rise to a similar stem, that of 

 the Ostracoda, while at a more recent date it once more gave 

 off a lateral branch in the shape of the Cladocera *. A 

 further point in agreement with the theory that the Cladoceran 

 stem did not arise until a later period is the existence of an 

 intermediate series leading to the Cladocera and consisting of 

 different genera of Estheridse {Limnadia^Limnetis)^ while all 

 other groups of Crustacea appear to be sharply separated from 

 the Euphyllopods at present living. 



According to these conceptions it is possible to establish a 

 natural system of classification among the Crustacea of which 

 the Entomostracan group is composed, from which there also 



* This is probaljly the best place to quote the following statement by 

 Dohrn (' Geschichte des Krebstammes,' p. 132), since we may gather 

 from it that Dohrn asked himself the question how the existing Euphyl- 

 lopod types are related to the other Crustacean groups in respect of 

 phylogeny. The passage in question runs as follows: — "But however 

 it may be with regard to Gigantostraca and Trilobites, in any case the 

 order Phyllopoda remains the matrix for all other forms of Crustacea at 

 present in existence. It is true that there is no way leading us into one 

 of the other orders either through Apus or through Branchipus^ but from 

 Nehalia as well as from the sheli-beai'ers we have to follow the com'se of 

 the development of powerful series of forms." 



34^ 



