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 tiic anterior margin of 

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

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

 lopment of the rostral f)late of the Stomatopods is connected 

 witli the segmenting off of the anterior part of the head, which 

 bears the eyes and the tirst antennte. I would at any rate 

 regard it as an heirloom from Nehalia, which lias been pre- 

 served with a peculiarity in the formation of tlie 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 (ce|)lialic valve), or at 

 least a corresponding process, developed for the protection of 

 tiie stalked eyes, probably also formed part of the primitive 

 Branchipus-s[\c\\, and that this was no longer developed 

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

 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. Finally, it must be further remarked that Clans f 

 has expressed himself in opposition to a homologization of the 

 cephalic valve of Xtbalia with the rostrum of the Malaco- 

 stracan shell \. 



Summary and Conclusion. 



In the preceding pages the attempt has been made to refer 

 the Cru.stacca 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 |)resent 

 day, namely, -Z>r(/«c/(/y;»,*, ^y'«/5, and Estheria. On making a 

 comparison between the most essential characters in the 

 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, loc. cit. pp. 133 & 142. 



t Claus, " Ueber den Organismus der Xebaliden, &;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 justiliable the homologization of the 

 cephalic valve of Xebalia with the rostrum of the Copepods, to which G. 

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

 during the years 1873-1870:'' 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 haa 

 arisen entirely independently in the Copepod group. 



Anil, it Mag. S. Hist. Ser. 6. ]'ol. xi. 34 



