314 ON THE CLASSES OF THE 



to doubt his having given much attention to this part of 

 natural history. 



In assio-ning however this place between the Annulosa 

 and liadiata to the Cirripeda, I confess that there are 

 many difficulties which, from my being unacquainted 

 with the anatomy of the Rudiata except from the de- 

 scriptions of others, I am unable at present openly to 

 encounter. For instance, Cuvier, Lamarck and all the 

 great modern zoologists place the Echini at the head 

 of the Radiata as possessing the most complicated struc- 

 ture ; yet, while Spix and others have been able to 

 detect aiiervous system in the listerias, they have utterly 

 failed in observing it among the Echini — " ce que j'at- 

 tribue" says M. Lamarck, "a des dispositions par licu- 

 lieres de ces parties dans les oursins, car je ne doute pas 

 qu'elles n'y existent" What apparently adds to this dif- 

 ficulty is, that the nervous system detected in the Asterias 

 bears no affinity whatever to that of the Annulosa and 

 Cirripeda. In the Sessile Cirripedes we may observe the 

 feet and all the other parts of the articulated inhabitant of 

 the calcareous tube gradually to diminish. Now as it is this 

 body which contains the nervous system of a Cirripede, per- 

 haps its. absolute disappearance in Echini may account 

 in some measure for the impossibility of detecting a ner- 

 vous system in these. This is an hypothesis it is true, but 

 it coiTesponds at least with the manner in which great 

 changes of structure are produced in nature. The spinal 

 marrow and the spine itself become gelatinous in the Gas- 

 trobranchus and the lower tribes of fishes, before we pos- 

 sess in their place the knotted nervous system of the An- 

 nelides. If the change from the nervous system of the 



