a particular instance, that I have but little doubt that five or six _species_ (so called) might have been recorded out of one, had only a few stray specimens been brought home for identification, without any regard having been paid to the respective circumstances under which they were found[33]." That "one," Protean, representative is the _Ptinus albopictus_, Woll.; and it is so eminently a case in point, that it may be admissible to quote, _in extenso_, a few of the observations which I have already published concerning it:-- "The _P. albopictus_ is the commonest of the Madeiran _Ptini_, and by far the most variable, having a separate radiating-form for almost every island of the group,--whilst, at the same time, the whole are so intimately connected together (and merge into each other) by innumerable intermediate links, that it is impossible to regard them, in spite of the opposite contour of the _extremes_, in any other light than as different aspects of a single species, according as circumstances may favour, retard, or otherwise regulate its development. Instability in fact (in its broadest sense) may be considered to be one of its most prominent characteristics, since it appears to be more sensitive to isolation and altitude than any of the other members of the genus with which we have here to do,--as may be proved to a demonstration by a careful study of its habits on the spot, where the influences of position and exposure are, in nearly all instances, more than sufficient to account for the successive phases assumed. Thus, commencing with _var._ alpha, which reaches its maximum in the sheltered ravines of the central mass, the bulk is usually large, and the tints comparatively intense. _Var._ beta. is likewise brightly variegated, but it is smaller. Now, if our premises be correct, that locality and the action of the external elements have much to do with the changes in question, we might have expected, _a priori_, that this state, from its peculiarity to the Dezerta Grande, would not only have reduced in dimensions (which it is), but in colour also (which it is not). Here, therefore, observation, _in situ_, becomes extremely important; since such does at once convince us that its almost exclusive attachment to the interior of the stalks of the _Silybum Marianum_, Grtn. (the _Holy Thistle_ of the ancients), with which the more protected portions of that island everywhere abound, affords it ample conditions, even on so bleak a rock, for its completion. Nevertheless, its _stature_ (as already stated) is slightly diminished in spite of this: and when we come to examine the individuals which infest the lichen of more open situations (aberrant however on the Dezerta Grande, and answering to the _var._ gamma. of the diagnosis), we immediately perceive that _both_ of our required results are indicated,--the reduction not being limited to size, but extended also to hue. In Porto Santo this