14 MALACOZOA. 



The vast series of animals destitute of a brain and 

 spinal cord, protected by a skull and vertebrae, has, by 

 Cuvier and many other Zoologists, been considered as 

 naturally divisible into three distinct portions, forming, 

 as it were, three different types of organization. To these 

 three groups have been given the names of Mollusca, 

 Articulata, and Radiata, or Soft Animals, Jointed Ani- 

 mals, and Rayed Animals. The Greek terms Malacozoa, 

 Entomozoa, and Actinozoa, also employed to designate 

 these groups, are more appropriate. 



The Malacozoa, although some of them approach 

 more nearly in structure to the Osteozoa or Vertebrata, 

 are, as a whole, inferior in their organization and 

 faculties to the Entomozoa, but superior to the Actino- 

 zoa, and may therefore be viewed as forming the third 

 type or series of the animal kingdom. 



Considered with respect to their external form, the 

 Malacozoa vary extremely, insomuch that no general 

 idea can be given of it. Their internal parts are always 

 soft, although, in a small number of them, there are 

 some solid internal pieces intended for the protection of 

 certain organs. Their nervous system is composed of 

 ganglia and nerves . The principal mass of these ganglia, 

 which may in some respects be compared to the brain, 

 forms a kind of collar round the oesophagus, and other 

 ganglia are dispersed through the body, but not in sym- 

 metrical order, nor forming a chain, as in the Entomozoa. 

 A few species have organs analogous to the ear ; many 

 are furnished with eyes ; but it is not certain that any 

 have a particular organ for smell ; and it appears that, in 

 very many of them, there are no other organs of sense 

 than those subservient to touch and taste. The organs 



