Classification of the Crustacea. 459 



quently proceeded from the flat shell. This being so, still 

 less do we meet with any difficulty in deriving the formation 

 of the shell of the Cirripedes from the shell of Apus. 



The Cirripede shell is, however, only apparently bivalve, 

 and its similarity to the Ostracod shell in the so-called Cijpris 

 stage is merely external. From the condition of the shell in 

 this stage its agreement with the shell of Apus can still be 

 demonstrated in spite of the external dissimilarity. A closer 

 consideration of the shell in the Cypris-Y\kQ, larva shows that 

 the shell is anteriorly directly continuous with the anterior 

 margin of the head. 



Thus it also comes to pass that the right and left portions 

 of the shell are united on the ventral side in the anterior half 

 of the animal, and the cleft which leads into the mantle- 

 cavity only commences far back. The shell of the Cirri- 

 pedes is consequently an undivided one, as in Apus, merely 

 extending backwards in direct continuation of the anterior 

 margin of the head. It would therefore be advisable not to 

 call the Cirripede shell bivalve, but to exclusively apply to it 

 the often-used term " mantle-shaped " (" mantelformig "). 



With reference to the common origin of Copepods and 

 Cirripedes, which results from the foregoing, it only remains 

 to discuss the mouth-parts of the latter, on account of their 

 different formation from those of the Copepods. The shape of 

 the mouth-parts of the Eucopepods, such as Cetochilus, which 

 have to be cited in this comparison, exhibits primitive con- 

 ditions, as has already been shown. In the Cirripedes, on 

 the other hand, the mandibles are devoid of palps, while the 

 two pairs of maxillte which follow them appear reduced and 

 developed in such a way that the similarity of the mouth- 

 organs to those of the Euphyllopods is certainly great. From 

 this circumstance a decided difficulty would result as regards 

 a common derivation for the Copepods and Cirripedes, and it 

 would be an argument in favour of a separate origin of the 

 Cirripedes from the Archiphyllopods if this similarity of the 

 mouth-parts were to be explained as being due to direct 

 inheritance ; in addition to this there would be the fact that, 

 while for the Archi])hyllopod ancestral form of the Copepods 

 the possession of palp- bearing mandibles and maxillae in the 

 shape of foliaceous feet is to be presupposed, the Cirripedes 

 would have to be derived from forms in which the formation 

 of the mouth-parts which is characteristic for all existing 

 Euphyllopods must already have appeared. Taking into 

 consideration the great agreement between the Cirripedes and 

 Copepods in, as it seems to me, more important characters, 

 the similarity in development between the mouth-organs of 



