260 ON THE CLASSES OF THE 



Octopus to be the type of the form, when we observe its 

 activity and the complete adaptation of its extraordinary 

 stru<;ture to its manner of Ufe ; and it is to the other animals, 

 which deviating from this construction seem to be de- 

 stined to inactivity, that we are to look for the means of 

 quitting the group for that division of animals which to us 

 must always be the most interesting on account of our- 

 selves forming part of it. 



Vertebrata. 

 Commencing with the Chelonian Reptiles, the naturalist 

 enters on this group remarkable for three things, the per- 

 fection of its organization, the great size of the individuals 

 which compose it, and the paucity of species which it con- 

 tains, when compared with the group oi Annulosa. Bones 

 constitute the great characteristic of the Vertehrata ; and 

 it is accordingly with the examination of them that we 

 ought to commence their study. In reptiles the bones are 

 particularly cartilaginous ; and, according to Caldesi, they 

 have no medullary cavity in tortoises, thus affording an ad- 

 ditional proof that what takes their place m the Cephalopoda 

 is the dorsal horny lance. Still the cartilaginous envelope 

 for tlie brain in the Cuttlefish is now become in the Tor- 

 toise a true osseous cranium. The neck has now seven 

 cei-vical vertebrae to support it, the two last of which be- 

 come anchylosed at a certain age. The upper shell or 

 carapace, to which we have before alluded, will be dis- 

 covered on minute examination to be formed by the ex- 

 pansion of eight pairs of ribs, which are anchylosed toge- 

 ther by real sutures, and united to a row of square osseous 

 plates which run along the middle of the back, so as to 

 form one solid inflexible piece. These osseous plates are 



