The total number of teeth in a rabbit is:

Structural organisation in animals attains different levels as cell-organ-organ system. What is missing in this chain? Mention the significance of such an organisation.

Identify the correctly matched pairs of the germ layers and their derivatives.
$I.$ Ectoderm - Epidermis
$II.$ Endoderm - Dermis
$III.$ Mesoderm - Muscles
$IV.$ Mesoderm - Notochord
$V.$ Endoderm - Enamel of teeth

Which one of the following lists contains only mesodermal structures?

Based on cellular mechanisms,there are two major types of regeneration found in animals. Which one of the following is the correct example of the type mentioned?

$Pheretima$ $posthuma$ and $Periplaneta$ are similar in which aspect?