Classification of the Crustacea. 441 



Apus is an example is to be found in the Copepoda and in 

 their allies the Cirripedia ; and that the Ostracoda in many- 

 respects exhibit characters of Estheria, not to speak of the 

 Cladocera, whose close affinity to Estheria will not be 

 disputed. 



In addition to this there came the conviction that the 

 present grouping together of the lower Crustacea as Entomo- 

 straca, as opposed to the Malacostraca, does not betoken a 

 natural arrangement. 



All these points led me to inquire whether, as a matter of 

 fact, Branchipus ought not to be regarded as a remnant of 

 the Archi-Phyllopod series, from which the Malacostraca have 

 sprung, while a similar remnant is represented by Apus in 

 the case of Copepods and Cirripedes, and by Estheria in that 

 of the Ostracoda, and at all events in all probability of the 

 Cladocera ; and whether, in the event of an affirmative 

 answer to this question, an attempt should not be made to 

 establish a more natural system of classification among the 

 Crustacea composing the group Entomostraca. 



In discussing this question we shall in the first place have 

 to compare one with another the three Euphyllopod types 

 above mentioned, as well as the peculiarities of the different 

 Crustacean orders. For the purposes of such a consideration 

 it will suffice to institute a comparison between merely the 

 most primitive forms in each individual order. 



As regards the structure of the Crustacea material is avail- 

 able in abundance in the shape of a voluminous literature, 

 which, however, I do not intend to quote in full in this paper; 

 in the present communication only a certain number of publi- 

 cations will be cited, and in the first instance such as demand 

 closer consideration with reference to my views. 



The Euphyllopoda. 



Among the Euphyllopoda the Branchipus-type appears to 

 be the most primitive, although again many of its peculia- 

 rities must be regarded as having been secondarily acquired. 

 Among the primitive characters must be mentioned the elon- 

 gated form of the body, the fin-like development of the furca, 

 which is beset with setge along its entire margin, the situation 

 of the eyes upon stalks, the similar development and the form 

 of the thoracic appendages, and the prolongation of the heart 

 throughout the whole of the body-segments ; on the other 

 hand, a secondary character is seen in the absence of a shell, 

 which originally must also have been present in the ancestors 

 of Bra7ichipus ; of a secondary nature again is the smaller 



