452 Prof. K, Grobben on the Genealogy and 



and among these represent a special group which contrasts 

 with all others, was first demonstrated in a convincing fashion 

 by Glaus *. Above all the transformation of the oral appen- 

 dage which is the homologue of tlie second maxilla into a 

 double pair of maxillipeds, as is characteristic of the Gopepoda, 

 and then also the shape of the feet in the larval stage, may 

 here suffice as important arguments. 



But we also observe in the Branchiura manifold Phjllopod 

 characters, which have always forced themselves upon the 

 notice of investigators. Nevertheless, as for me, my first 

 concern in this question is to inquire whether tlie Branchiura 

 admit of comparison with existing Euphyllopods, and, if so^ 

 with which of them. That it is the Apodidae, and these 

 alone, that offer themselves for a closer comparison will appear 

 from what follows. 



The first resemblance between Argulidee and Apodidas 

 which strikes us is seen in the shield-shaped development of 

 the cephalothoracic carapace, which, in the case of Argulusj 

 covers the three anterior segments of the thorax. This shield 

 is continued as in Apus into the anterior margin of the head. 

 Especially when we select for comparison the formation 

 of the cephalothoracic shield in the larvte of Apus the extensive 

 agreement forces itself still further upon us. Glaus was also 

 struck by this resemblance, and with reference to it we find in 

 his previously- quoted paper upon Argulus^ in connexion with the 

 comparison of the Argulidaj with the lSiphonostomata,thefollow- 

 ing passage f: — " Should we wish to bring forward Phyllopods, 

 in order to derive the Argulid form from them, we should be 

 confined to the shield-shaped larvee of Apus, whose mouth- 

 parts are devoid of the maxilliped structures which are so 

 characteristic of the Gopepoda, and in conjunction with the 

 foot-rudiments already bear the character of the Phyllopods. 

 Nevertheless this comparison would in itself be morphologi- 

 cally apt, since in the shield-shaped dermal expansions of the 

 parasitic Gopepoda and of the young Phyllopoda we recognize 

 equivalent structures." It is precisely upon the great resem- 

 blance in formation between the cephalothoracic shield and 

 that of Apus that I would here primarily insist. 



But there is yet a further peculiarity to be mentioned which 

 Argulus has in common with Apus, and that is the possession of 

 the compound lateral eyes, which, as in the case of Apus, 

 appear to be sunken and covered by the skin. After finding 



* C. Glaus, " Ueber die Entwicklung, Organisation, und systematische 

 Stellung der Arguliden," Zeitschr. f. wiss. Zool. Cd. 26, 1875. 

 t Glaus, he. cit. pp. 4, 5. 



