292 CLAUS^ ON THE 



But as almost all tlieories respecting the limbs, which have 

 been propounded in the case of the Arthropoda, have broken 

 down from the circumstance that the original equivalence of 

 the whole body has been assumed a priori for all the Arthro- 

 poda^ or, at any rate, for considerable sections of them, and 

 the observed modifications made to fit into the scheme so 

 constructed ; so the fault of every observer has consisted in 

 this, that they have imagined all the Crustacea to be seg- 

 mented according to the same plan, and have consequently 

 taken the number of segments in the Malacostraca as explana- 

 tory of the entomostracan structure. If we wish to arrive at 

 a correct theory of the limbs, we shall have first to obtain, in 

 each case, the proof from development that a similar plan is 

 followed in the construction of the body, and shall have to 

 set out from groups of limited extent, and in these to trace 

 the identity of structure, before we can arrive at more general 

 results. 



Milne - Edwards and Audouin have drawn the parallel 

 between the limbs of Pandarus and those of the Decapoda ; 

 and have applied, in reference to the prehensile organs 

 (second antennae), the hypothesis first started by Oken, that 

 the jaws were feet advanced towards the head. They 

 declared that the maxillary organs existing in and around the 

 suctorial proboscis (composed of the labium and labrum) were 

 the equivalents of the mandibles and two pairs of maxillee ; 

 the hook-like clasping organs to be the backwardly placed 

 first pair of maxillary feet ; the four clasping-hooks anterior 

 to the eight, and thoracic feet, as the second and third pairs of 

 maxillary feet, assuming at the same time the abortion of the 

 second antennse. 



Erichson probably had this attempt at an explanation 

 before his mind when he formed his scheme from the limbs 

 of the Hexapoda, which, according to him, was to be found 

 repeated in subordinate modifications in all the other groups 

 of Arthropoda, and which, in the case of the Entomostraca, he 

 employed by regarding the second antennae of Cyclops as 

 advanced thoracic feet. 



The views of Audouin and Milne-Edwards^ respecting the 

 oral organs of Pandarus and the Siphonostomata, otherwise 

 met with no general reception. Rathke was as little disposed 

 to agree with them as Burmeister, who very properly assigns 

 to the Entomostraca their own place among the Crustacea ; 

 whilst Van Beneden, and even Gerstacker (" Beschr. zweier 

 neuer Siphonostoraen," Troschel's 'Archiv,^ 1854), it n-ould 

 seem, without adducing any proof, held the opinion that the 

 second antennae were advanced jaw or thoracic feet. But 



