Question

a) Write a note on nervous system in leech. (3 Marks)
b) Why is the teeth of rabbit called heterodont? (4 Marks)

Answer 1

a) The nervous system in leech:

• The central nervous system of leech consists of a nerve ring and a paired ventral nerve cord. (1 Mark)
• The nerve ring surrounds the pharynx and is formed of suprapharyngeal ganglion (brain), circumpharyngeal connective and subpharyngeal ganglion. (1 Mark)
• The subpharyngeal ganglion lies below the pharynx and is formed by the fusion of four pairs of ganglia. (1 Mark)

b) Dentition in rabbit:

• In rabbit the teeth are of different types. Hence, the dentition is called heterodont. (1 Mark)
• There are four kinds of teeth in mammals. They are incisors (I), canines (C), premolars (PM) and molars (M). (1 Mark)
• This is expressed in the form of a following dental formula:
  (1 Mark)
• Dental formula represents the number of each kind of tooth in the upper and the lower jaws on one side of a mammal. (1 Mark)