CEPIIALOrODA. 613 



parts of the animal organisation. In our past review of the Invei*te- 

 bratn, we have witnessed this order in the appearance of the more 

 essential organs, as the nervous centres, the eyes, the stomach, the 

 heart, the gills, the generative parts ; Ave find it equally regulating 

 the development of the peculiar prehensile instruments of the Cepha- 

 lopodic class. 



At first very numerous, comparatively small and feeble, essen- 

 tially alike, the cephalic tentacles of the Nautilus strikingly illus- 

 trate the law of vegetative or irrelative repetition. Their primary 

 import is, however, plainly indicated by the direct derivation of their 

 central nerve from the anterior cephalic ganglion ; and they present 

 the same complex- plan of arrangement of their muscular fibres which 

 characterises the arms and tentacles of the dibi-anchiate Cephalopods. 

 The prehensile surface of the tentacula of the Nautilus {^Jig- 214.) is 

 made adhesive after the type of the simple laminated sucker of the 

 Remora ; the median longitudinal impression which partially divides 

 the lamella may represent the complete interspace which separates 

 into two series, in the arms of most of the Dibranchiates, the more 

 complex suctorial appendages which are developed on their internal 

 surface : but at all events, the reduction of these arms in number, 

 their augmentation in size, and perfection as prehensile instruments 

 by the superadded complications, are phenomena which ordinarily 

 attend the march of development. The order of this progress 

 would be anomalously reversed if the tentacles of the Nautilus repre- 

 sented, as M. Valenciennes supposes, the caruncles of the acetabula, 

 and the hollow processes of the oral sheath the cavities of those 

 appendages of the arms of the Dibranchiates. According to the 

 French Malacologist, the anterior circumference of the head or oral 

 sheath in the Nautilus represents four of the eight arms developed 

 therefrom in the Dibranchiates, and the two dorsal arms consist each 

 of two enormous acetabula, whose cavities are deepened into tubes, 

 and whose caruncles are produced into tentacula as highly organised 

 in regard to their nerves and muscles, as are the acetabuliferous 

 arms themselves in the higher orders. The four other arms of the 

 Octopus are represented, according to M. Valenciennes, by the four 

 groups of tentacula which are included within the oral sheath in the 

 Nautilus. Such is not, however, the place of origin of any of the 

 eight arms in the Dibranchiata ; nor is it conformable with the ge- 

 neral law of development, that a prehensile organ consisting of two 

 large and highly complicated acetabula in a low organised Cephalopod 

 should suj)port two hundred smaller and more simple suckers in the 

 higher organised species.* 



• CCCCIII. 



R II 3 



