Both combination and subdivision are intended to facilitate identification, by aiding us to arrive at this knowledge of species; for each species represents a distinct idea, whose correct definition is important to the progress of accurate science. This alone permits observation to be attributed to its right object, and when properly recorded, the information is secured for ever from error or obscurity. It is not, however, the gift of every mind to discern accurately even specific differences, or to form skilfully generic combinations. The very best favoured by nature,—for it is a natural gift, although under high cultivation,—have sometimes a bias towards seeing more than actually exists. Hence varieties are often elevated into species, and species thus overwhelmingly multiplied; and genera are frequently framed upon vague distinctions. Species are the basis of all natural science. A species in zoology is a combination of creatures which unites the sexes, and these being two, the assumed existence of neuters in some instances does not invalidate this, it comprises two individuals having independent existence, but whose co-existence is indispensable to perpetuation, but which often, from their great differences, no single set of scientific characters will bind together, yet which must exist in some undiscovered peculiarity, that individuals may be able to distinguish their legitimate partners. The species, therefore, is a complete unit in its entirety, although consisting of two distinct beings, for in the large majority of cases in zoology these sexes are distinct, although their conjunction is, in the higher forms of life, indispensable for their continuance. In some of the lower forms of animal life they exist in union, and in the vegetable kingdom we perceive every possible combination and modification of this conjunction, and in both of these life may be perpetuated also by simpler processes. The species may consist of any indefinite number of individuals, and no law has hitherto been discovered which regulates the relative proportions of the sexes, although it is very apparent that some recondite influence operates to control it. It is also extremely remarkable to observe how eccentric nature is in some species, and the extent to which she sometimes carries the variation of some particular specific type, and to which some species are singularly prone, and yet how rigidly in other cases she adheres to the particular specific form in the succession of generations, that even the shadow of a deviation from the typical distinction is scarcely to be discovered: a reason for this it is hard to surmise. We may, nevertheless, conclude it to be certain that true species are ever distinct, and can no more coalesce, however closely they may approach together, than can asymptotes.