EIGHTH BRANCH OP ZOOLOGY. 



MALACOLOGY. (Gr. fialaxos, malakos, soft ; ttyo$, logos, 

 discourse.) 



THIS is the science of the structure and habits of soft animals, 

 or Mollusks. Many of these, from the number, variety, and beauty 

 of their shells, invited attention at an early period, under the 

 name of CONCHOLOGY, (Gr. konche, a shell ; logos, a discourse ;) 

 but in order to a natural classification, and a knowledge of the 

 habits of the class, it was found that the entire animal must be 

 known ; hence, Conchology has been merged in MALACOLOGY. 



THIRD SUB-KINGDOM. MOLLUSC A, (Lat. moths, soft.) MOLLUSKS. 



The Mollusks are, as a whole, inferior to the Articulates in 

 their organization and faculties, but yet are superior to the Ra- 

 diates, thus ranking as the third series in the Animal Kingdom. 



In their external form, they are exceedingly various. Their 

 internal parts are always soft, fleshy, moist, and cold ; although 

 a small number of them have some solid internal pieces intended 

 for the protection of certain organs. The nervous system, in- 

 stead of being developed in the form of a spinal cord, is com- 

 posed of ganglia and nerves, which are dispersed, more or less 

 irregularly, in different parts of the body. A few species have 

 organs analogous to the ear; many are furnished with eyes; but 

 it is not certain that they possess any sense of smell. Many of 

 them appear to have no other organs than those subservient to 

 touch and taste. The sense of feeling is probably most acute in 

 the tentacula. The organs of sense and locomotion are generally 

 arranged with symmetry. The muscles are attached to the 

 skin ; and by the alternate elongation and contraction of certain 

 parts, the animals crawl on the ground, swim on the water, and 

 lay hold of objects; but, as their limbs are not supported by 

 bones or other solid parts, their motions are usually very slow. 

 They are never furnished with feet arranged in series on each 



