In three specimens of an Arvicola he found the gall-bladder having a very different degree of development, and there is reason to believe it is sometimes absent.

Professor Owen has shown that this is the case with the gall-bladder of the giraffe." Dr.Crisp (_Proc.Zool.

Soc._, 1862, p.

137) found the gall-bladder present in some specimens of Cervus superciliaris while absent in others; and he found it to be absent in three giraffes which he dissected.

A double gall-bladder was found in a sheep, and in a small mammal preserved in the Hunterian Museum there are three distinct gall-bladders.
The length of the alimentary canal varies greatly.