454 Prof. K. Grotben on the Genealogy and 



the nervous system and digestive organs once more show 

 resemblances to the conditions among the Euphyllopods. 



In the organization of Argulus we consequently find pecu- 

 liarities which remind us of Apus among the Phyllopods, 

 while we also meet with Copepod characters, and, lastly, 

 points of resemblance to the Cirripedes. For our present 

 consideration the yi;?«s-cliaracters are of the first importance; 

 we shall have to revert to the others again later on. 



On submitting the characters of the Eucopepoda to exami- 

 nation with reference to the question under discussion, we 

 meet with great difficulties at the first glance. 



The segmentation of the body in the Eucopepoda is 

 more extensive than in Argulus. While all segments are 

 fully developed, as is seen also in the Calanidse, the most 

 primitive of Eucopepods, we find that in addition to the head 

 five thoracic and five abdominal segments are present. In 

 this respect, in comparison with the Branchiura, the Eucope- 

 pods exhibit a more primitive condition. 



On the other hand, the cephalothoracic shield, which in 

 Argulus is of fairly large proportions, is only extremely feebly 

 developed in the Eucopepoda, and has undergone degenera- 

 tion, no doubt in connexion with the rapid locomotion of these 

 pelagic animals, for which a large carapace would be in no 

 case of advantage. If we compare it with the shell-structures 

 of the Euphyllopods we soon come to the conclusion that the 

 cephalothoracic shield of the Eucopepods can only be referred 

 to the shield of Aims. As in the case of Apus and also in 

 Argulus, the edge of the rudimentary lateral reduplicature 

 forming the cephalothoracic shield of the Eucopepods is con- 

 tinued into the anterior margin of the head. In general this 

 condition appears more distinctly in the Nauplius-larvaj of the 

 Eucopepoda, which also in other respects exhibit Euphyllopod 

 characters, since moreover the shield of the Nauplius some- 

 times still possesses a broad flat shape. The flat develop- 

 ment and the mode of connexion of the cephalothoracic shield 

 with the anterior margin of the head already referred to belong 

 to the .4;t??/s-character. 



In the formation of the cephalic appendages the Eucope- 

 poda exhibit more primitive conditions than the Branchiura. 

 Here again it is the Calanidai which will have to be con- 

 sidered. The first antenna in the Calanida3, as in all free- 

 living Copepods, is very long and serves for locomotion. Its 

 colossal size in comparison with its original development as a 

 sensory antenna and its utilization as an organ of locomotion 

 are, like the analogous development of the first antenna among 

 the Ostracoda, to be considered as of a secondary nature. 



