472 On the Genealogy of the Crustacea. 



With reference to the Euphyllopods, there is, however, a 

 difficulty still to be disposed of. If the views which I have 

 here t«tt down are correct, and in the existing Crustacea are 

 to be seen the descendants of three Archiphyllopods wliich 

 differed in outward form and may be met with again in the 

 three types, Branchipus, Apus, and Estheri'a, what is the 

 explanation of the fact that in these three representatives of 

 old ancestral forms, which have at any rate existed side by 

 side for a long time separated in three series of forms of 

 different halilus, the degeneration of the mandibular palp and 

 the reduction of both maxillse is to be found in the same 

 manner ? That the peculiar development of the mouth-parts 

 in existing Euphyllopods is a secondary character will not be 

 questioned any more than the assumption that the old ancestral 

 forms possessed mandibular palp and maxillas like foliaceous 

 feet, as is evident from the existence of such mouth-parts in 

 the case of the Ostracoda, Copepoda, and Malacostraca. 



In my opinion the degeneration of the mandibular palp, 

 as well as the diminution in size of the maxillse in the Bran- 

 chipus-, Apus-^ and Esthena-aeries of Euphyllopods, took 

 place independently, and are to be explained as an instance of 

 convergence. This convergence finds a further explanation 

 in the origin of the three series alluded to from a common 

 primitive form, in which there existed a similar tendency to 

 development in the directions indicated. Moreover we find 

 that the degeneration of the mandibular palp is of frequent 

 occurrence, as in the Cyclopidse among Copepods and also in 

 the Cirripedia, which latter also possess maxillteof a diminished 

 size. 



In so far as a proof can be given I have endeavoured to 

 give it, in order to establish the view that the three Euphyllo- 

 pod types at present existing, which are so very divergent 

 from one another in external structure, are remnants of three 

 ancient Archiphyllopod series to which the rest of the Crus- 

 tacea now living can be traced back. The changes in the 

 system of classification are merely the result of these views. 



That much that was already known has been repeated in 

 the course of the argument cannot be made a subject of 

 reproach against this consideration of the question, since it is 

 chiefly a case of fresh combination of known facts. Neither 

 can blame be attached to the omission to notice many systems 

 of organs, since many of these furnish no points for my argu- 

 ment. It is self-evident that only those organs could be 

 brought forward in which sufficient differences in formation 

 appear with reference to their resemblance to the three 

 Euphyllopod types. 



