Within the digestive system, the form of the teeth (whether they are incisors or molars) varies with the 'length, convolutions, and dilations of the alimentary system'; or again, as an example of coexistence between different systems, the digestive organs cannot vary independently of the morphology of the limbs (and especially of the form of the nails); according to whether they will be provided with claws or hoofs and therefore whether the animal will be able to grasp and tear up its food or not so the alimentary canal, the 'dissolving juices', and the form of the teeth will also differ.