CHAPTER II. Fact of Variation As a matter of experience As probable from analogy CHAPTER III. Causes of Variation Sec. 1. Climatal causes generally (whether dependent upon latitude or upon altitude) Sec. 2. Temporary heat or cold, of an unusual degree Sec. 3. Nature of the country, and of the soil Sec. 4. Isolation; and exposure to a stormy atmosphere CHAPTER IV. Organs and Characters of Variation CHAPTER V. Geological Reflections CHAPTER VI. The Generic Theory CHAPTER VII. Conclusion CORRIGENDUM. Page 90, for _Pecteropus Maderensis_ read _Pecteropus rostratus_. SPECIFIC VARIATION IN THE INSECTA. CHAPTER I. INTRODUCTORY REMARKS. A very small amount of information gained by the student in the field of Nature is sufficient to kindle the desire to increase it. The more we know, the more we are anxious to know; though the less we seem to know. It is one of the distinctive privileges of the naturalist that he has to labour in a mine which is inexhaustible: the deeper he digs beneath the surface, the richer is the vein for excavation, and the more interesting are the facts which he brings successively to light. Dive he ever so deep, Truth, "at the bottom of the well," is assuredly present, under some form or other, to reward him still; nor will she even for once elude his grasp, provided he be content to receive her as she is, instead of endeavouring to mould her to his preconceived ideas of what she ought to be. In these times of patient research, when the microscope is disclosing, day by day, fresh wonders to our view, and new lines of speculation are springing out, as it were spontaneously, from the regions of thought, it is remarkable that many of the commoner questions relating to the members of the external world around us have remained comparatively unsolved; nor indeed have some of them ever been discussed at all, except in a desultory manner and with insufficient data to reason from. Foremost amongst these, numerous problems affecting the distinction between "varieties" and "species" (as usually accepted) of the animal kingdom stand pre-eminent,--especially in the Annulose Orders, in which those distinctions are less easy, _a priori_, to pronounce upon.