458 Prof. K. GroTbben on the Genealogy and 



Apns can be sliown to exist, and they are to be looked for 

 in the first instance in the Nauplius conditions. The Nauplius 

 of the Cirripedes agrees with that of the Phyllopods, and 

 among these with that of Apus, even more than with the 

 Copepod Nauphus. As Apus-Vike cliaracters I may point 

 out the shield-shaped expansion of the shell, which is directly 

 continuous with the anterior margin of the head, and more- 

 over the presence of the compound lateral eyes, which, as in 

 the case of Apus, lie beneath the integument. The lateral 

 eyes have separated from the skin and are deep-seated, and 

 consequently in this respect they agree with the rudiments of 

 the lateral eyes of the Eucopepod Nauplius (and probably also 

 ofAfffuIus). As in the latter case, so in that of the Cirri- 

 pedes, I regard the separation of the eyes from the skin and 

 their downward change of position as a modification of the 

 process observed in Apus, where the eye is overgrown by the 

 integument. In the so-called Gypris stage of the Cirripedes 

 also the compound eye retains this position. 



If the comparison just instituted is correct we must expect 

 to find still more points of agreement with the Cirripedes in 

 the case of the Argulida^ than in that of the Eucopepoda. 

 This also is exactly what takes place. The paired lateral 

 eyes of Argulus, whicli have likewise passed beneath the 

 skin, are copies of the paired eyes of the Cirripede Nauplius. 

 The thoracic feet of Argulus show a similarity to the Cirri- 

 pede limbs, as has already been asserted by Claus, and also 

 the flagellum of the two first thoracic feet of Argulus might, 

 according to Claus *, be comparable to the lancet-shaped 

 appendage of the Cirripedes, in which case, however, it might 

 still correspond to an epipoclite. Argulus consequently does 

 not merely prove to be a form intermediate between the 

 Apodidse and Eucopepods, but also possesses the same signi- 

 ficance between Cirripedes and Copepods, In Argulus there- 

 fore we find a mixture of characters belonging to Copepods, 

 Cirripedes, and Apus. 



Since, as I think, an objection can hardly be raised to the 

 close afiinity of the Cirripedes to the Copepods^ we now arrive 

 at a solution of the question as to how we are to interpret the 

 bivalve shell of the Cirripedes. We must agree with Pagen- 

 stecher and Claus f in regarding the bivalve Cirripede shell 

 as a special adaptation from the shield-shaped rudimentary 

 shell as it appears in the Copepod Nauplius. It has conse- 



* C. Claus, ' Ueber die Eutwicklung, Organisation, &c. der Arguliden/ 

 p. 34. 



t C. Clans, ' Untersucliungen zur Erforscliuug der genealogischeu 

 Grundlage des Crustaceeusystems,' p. 83. 



