"Felix qui potuit rerum cognoscere causas" is a motto which the student of Nature should keep constantly in view; for it is undoubtedly a more honourable task to discover the _reasons_ for what we see, than the mere appearances themselves. He who has dived deeply into the everyday circumstances around him will be reluctant to ascribe so much as a single item of all that comes within his ken, to chance; for to him the whole system of created things is, from first to last, replete with design. _Natura nil agit sine causa_ is as true now as it ever was, and it will be so to the end. Let us not therefore be discouraged at the apparent smallness of the data from which many of our conclusions have to be drawn, for nothing is in reality trivial which is the effect of a wisely appointed law; and, even were such the case, it would not be thereby proved that the investigation of the law itself (however liable it may be to exceptions) is unimportant. Nor ought we, on the other hand, to be discouraged if we cannot always reconcile conflicting phaenomena, and detect in each a primary controlling cause. We should rather bear in mind, that the elements with which we have to deal are obscure, and subject to permutations from which various results must of necessity arise; and that it is only, therefore, on a broad scale that we can look for uniformity of action, even from conditions which may appear to be identical. "Nature is not irregular, or without method, because there are some _seeming_ deviations from the common rule. These are generally the effects of that influence which free agents, and various circumstances, have upon natural productions[45]." FOOTNOTES: [3] Religion of Nature Delineated, p. 103. [4] Journal of Researches (London, 1852), p. 381. [5] The great preponderance of the phytophagous over the predacious tribes, in the hotter regions of the earth, is a remarkable fact, and strongly suggestive of the relation which the insect and vegetable worlds (both of which attain their maximum in those zones) bear to each other. "The carnivorous beetles, or _Carabidae_," says Mr. Darwin, "appear in extremely few numbers within the tropics. The carrion-feeders and _Brachelytra_ are very uncommon; on the other hand, the _Rhynchophora_ and _Chrysomelidae_, all of which depend on the vegetable world for subsistence, are present in astonishing numbers. The orders _Orthoptera_ and _Hemiptera_ are peculiarly numerous; as is, likewise, the stinging division of the _Hymenoptera_, the bees, perhaps, being excepted."--Journal of Researches, p. 34. [6] Mr. Westwood states that he possesses an individual of the _Papilio Machaon_ from the Himalayan Mountains, captured by Professor Royle, "which scarcely exhibits the slightest differences when compared with English specimens."--_The Butterflies of Great Britain_, p. 4. [7] Zoologist, xiii. p. 4655. [8] The Butterflies of Great Britain (London, 1855), p. 17. [9] _Id._ p. 94.