1. The integumentary structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer layers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands.

3. In vivo, it is still not entirely clear how and which cell types cancer initiation occurs with solely loss of Rb, but it is clear that the Rb pathway is altered in large number of human cancers.[110] In mice, loss of Rb is sufficient to initiate tumors of the pituitary and thyroid glands, and mechanisms of initiation for these hyperplasia are currently being investigated.