Classification of the Crustacea. 465 



probably also homologous. So far as can be concluded from 

 the observations at present available *, it must be supposed 

 to arise by being segmented off from the anterior margin of 

 the cephalo-thoracic shield, just as also in the case of 

 Nehalia the cephalic valve arises in this manner. The deve- 

 lopment of the rostral plate of the Stomatopods is connected 

 with the segmenting off of the anterior part of the liead, which 

 bears the eyes and the first antenna. I would at any rate 

 regard it as an heirloom from Nehalia^ which has been pre- 

 served with a peculiarity in the formation of the head, or else 

 has developed again by a process of atavism. In the event 

 of this interpretation being correct, we may draw from it the 

 further conclusion that the rostral plate (cephalic valve) , or at 

 least a corresponding process, developed for the protection of 

 the stalked eyes, probably also formed part of the primitive 

 Brancliipus-^A^^W, and that this was no longer developed 

 among the Schizopods, as well as the forms arising from thera, 

 but that the portion equivalent to it is to be looked for in the 

 rostrum of the shell, which thereby acquires a heightened 

 interest from a morphological point of view. The possession 

 of a movable rostral plate is to be assumed for the Archi- 

 schizopods. I'inally, it must be further remarked that Glaus f 

 has expressed himself in opposition to a homologization of the 

 cephalic valve of Nehalia with the rostrum of the Malaco- 

 stracan shell %. 



Summary and Conclusion. 



In the preceding pages the attempt has been made to refer 

 the Crustacea which are united in the group Entomostraca, as 

 well as the Malacostraca, to the three types which are to be 

 distinguished among the Euphyllopods existing at the present 

 day, namely, Br anchipus, Apus, and Estheria. On making a 

 comparison between the most essential characters in tiie 

 different outward structure of these forms it has been found 

 that the Cladocera and Ostracoda can be referred to ancestral 

 forms resembling Estheria, while the Copepoda and Cirripedia 



* Cf. Claus, he. cit. pp. 133 & 142. 



t Claus, " Ueber den Organismus der Nebaliden, &c.," p. 39. 



X I feel bound to remark that, on the other hand, I, in accordance with 

 Claus {loc. cit.), do not regard as justifiable the homologization of the 

 cephalic Talve of Nehalia with the rostrum of the Copepods, to -which G. 

 O. Sars ("Report on the Phyllocarida collected by H.M.S. * Challenger ' 

 during the years 1873-1876:" The Voyage of H.M.S. 'Challenger,' 

 Zoology, vol. xix. 1887, p. 31) alludes. The so-called rostrum of the 

 Copepods has nothing to do with that of the Malacostraca, and baa 

 arisen entirely independently in the Copepod group. 



Ann. d: M'ag. N. Hist. Ser. 6. Vol. xi. 34 



