If one does not, in fact, arrange the species side by side in all their vast diversity, but, in order to limit the field of investigation forthwith, if one accepts the broad groupings evident at a first glance such as the Gramineae, the Compositae, the Cruciferae, and the Leguminosae for plants; or worms, fishes, birds, and quadrupeds, for animals it becomes apparent that certain characters are absolutely constant and occur in all the genera and all the species it is possible to distinguish: for example, the insertion of the stamens, their position in relation to the pistil, the insertion of the corolla when it bears the stamens, the number of lobes surrounding the embryo in the seed.