Fundamerital Types (rf Organization. ^ 



might be raised, if the principles were applied to the filling up 

 of all the gaps. 



According to my view, there are two great divisions of the 

 animal kingdom. The one consists of those provided with a 

 true spinal cord, inclosed within a shut vertebral column, which 

 is always wanting in the other. In the former, the whole brain 

 is situated above the pharynx, and inclosed in an osseous capsule, 

 the skull. In the other there is either a single cerebriform mass, 

 or several nervous knots united together by cords of nervous 

 substance surrounding the oesophagus. The mass analogous 

 to the brain is sometimes above, sometimes below this canal, 

 and is developed in an osseous or horny capsule, which separates 

 it from the other parts of the head ; and its posterior part gives 

 out no prolongation comparable with the spinal cord of the other 

 animals. This division, therefore, coincides with that of La- 

 marck into Vertehrata and Avertebrata. They might also be 

 called Cranial and Acranial animals. We shall, however, adhere 

 to the old epithets of Lamarck, to avoid overloading biology by 

 the introduction of new names. 



In all the vertebrata, the anterior extremity of the spinal cord 

 inclosed in the cranium, possesses the same form that it does in 

 man, and in all undergoes a considerable augmentation both in 

 mass and volume, compared with the rest of the cord. Even 

 from the numerical differences of this proportion, four classes 

 can be distinguished in these animals. I found the limits of the 

 proportional weights of the spinal cord to the brain to be, — 



In the first class from - - 1 : 85 to 1 : 6.5 



second, - - - 1 : 24.3 to 1 : 6.7 



third, - - - - 1 : 3.6 to 1 : 3 2 



fourth, - - - - 1 : 3.5 to 1 : 1.0 



The relation of the greatest breadth of the cord to the* great-- 

 est breadth of the brain ranges, — '*^ 



In the first class, from - - 1 : 6.85 to I : 1.20 

 second, . . - 1 : 4.45 to 1 : 1.12 

 third, - . - 1 : 2.55 to 1 : 1.35 



fourth, - - - 1 : 1.43 to 1 : 1.28 



'■• ■•• ' IQ .. 



V<M..,X,IlI.!Np.lXXy.r^JULY 183^. F ,^^ 



