Insecta

“ Nevertheless, we may briefly repeat, that, so far as the first is concerned, it is in islands that we detect the maximum of instability to which the wings of the Insecta are liable, and that it is in seasons of extraordinary heat that their development [Pg 99] is everywhere inclined (if at all) to be especially stimulated: whilst, as regards the second, it will be sufficient to state, that in continents, when any decided alteration takes place in the organs of flight, it for the most part comes to pass that an increased (rather than diminished) action is the result ”

“ I believe that, if analogies were more carefully studied in the lower departments of the animal kingdom, we should be less inclined to deny some sort of uniformity to the action of elements and conditions which, by a law of Nature, must at times operate equally upon the various and dissimilar members of the organic creation. Amongst the Insecta, where the individuals exist in such multitudes that accuracy in generalizations concerning them, becomes, as it were, peculiarly within our reach, this doctrine cannot be too rigidly insisted upon ”

“ In most cases of metamorphosis those organs of the larva, which are found also in the adult, persist through the transformation, undergoing merely the ordinary modifications of development. But it sometimes happens that such organs are completely destroyed and rebuilt during the metamorphosis. This is conspicuously the case in the metabolous Insecta, in some of which all the internal organs undergo disruption and are reformed. It happens also in those nemertine worms which develop by a larva ”

“ That positive and well-defined varieties, or races, should be confined to certain species, is not remarkable; but that every individual insect should differ, however slightly, from its nearest relation and ally, may perhaps require some few words of explanation, even to a naturalist. ”

“ The main object however of the present section being to show that a considerable amount of power is due to isolation itself, in regulating (after a long series of ages) the outward aspect of the insect tribes, it is not strictly necessary that we should so rigidly insist on deterioration of size as one of its primary consequences,—since (whether it be so or not) we are merely concerned here to demonstrate, that its influence, in some shape or other, is absolute and real. ”

“ But let us glance at the subject through the medium of an example, and endeavour to realize what would be the consequence of that wholesale combination at which we must sooner or latter arrive, if genera are not to be upheld because they slowly merge into each other as we recede from their respective types. The immense department Carabidæ, of the Coleoptera, is eminently a case in point. ”

“ The above examples, although few and indiscriminately selected, will serve to illustrate the principle which we have been contending for,—that climatal influences generally, may (and in most instances do) tend to affect, more or less directly, the outward contour of the insect tribes. ”

“ As an additional indication of the distinctness and isolation of the Neotropical region from all others, and especially from the whole Eastern Hemisphere, we must say something of the otherwise widely distributed groups which are absent. Among mammalia we have first the order Insectivora, entirely absent from South America, though a few species are found in Central America and the West Indies; the Viverridæ or civet family is wholly wanting, as are every form of sheep, oxen, or antelopes ”

“ Genus Esacus, Less. The genera Œdicnemus and Esacus are merely modifications of the same form; the variation in that of the bill being expressly adapted for procuring the kinds of food upon which the species respectively subsist; the Œdicnemus frequenting the stony deserts of the interior of the country feeds upon insects of various kinds, and the tender shoots of herbage; while the Esacus, resorting to the salt-marshes and the shores of the sea, lives upon crabs, mollusks and other marine animals. ”

“ However, it is usually recognized that the organization which colonies of these insects exhibit is an outcome of certain habits of cooperation which have become innate in the species through a process of natural selection in the course of a long period of evolution. In other words, the societies formed by ants, bees, and wasps are organ- ized upon the basis of instinct. ”

“ Because these building insects possess an innate geometry, an order of architecture which is known without being taught and which is constant in the same group, while varying as between one group and another. Just as much as the details of the organism, or perhaps even more so, this propensity to build according to certain determined rules characterizes the corporations known by the name of species. ”

“ In mixed colonies, on the other hand, which, in a state of nature, can be formed only by species of ants of close taxonomic affinities, the insects live together in a single nest and bring up their young in common. Although each of these categories comprises a number of dissimilar types of social symbiosis, and although it is possible, under certain circumstances, as will be shown in the sequel, to convert a compound nest into a mixed colony, the distinction is nevertheless fundamental. ”

“ We may also see these societies in what may be considered different stages of evolution; the phenomena we are alluding to being in some species much less marked than they are in others, and these more primitive kinds of societies being composed of a smaller number of individuals, which are also much less different from one another. We, moreover, meet with complex societies exhibiting some remarkably similar features among Insects that are very different systematically. ”

“ In arranging the species of a great natural order they are always divided into first large and then progressively smaller and smaller groups. The order is divided into coordinate families, each family into coördinate genera, and each genus into species which are also coordinate. Usually there are found to be more subdivisions than these and we have in botany at least, suborders, subfamilies, tribes, subtribes, and subgenera. Even species have their varieties, and in some sciences, particularly in ornithology, these are called subspecies and have a special significance. ”

“ But if in our diagram we suppose, for instance, the stigma to be seated at the bottom of a deep cavity, low down in the column, or the anther to be seated higher up, or the pedicel of the rostellum to slope more upwards, &c.—all of which contingencies occur in various species,—in such cases, an insect with a pollinium attached to its head, if it flew to another flower, would not place the pollen-masses on the stigma, unless their position had become greatly changed after attachment. ”

“ Kirby and Spence, in describing the societies of insects, say:—"But when we consider the object of these societies, the preservation and multiplication of the species, and the means by which that object is attained (the united labours and co-operation of perhaps millions of individuals) , it seems as if they were impelled by passions very similar to those main-springs of human associations which I have just enumerated. Desire appears to stimulate them, love to allure them, fear to alarm them. They want a habitation to reside in and food for their subsistence. ”

“ Whether such a separation be due to geographical barriers, to migration, or to any other state of matters leading to exclusive breeding within the separated group, I shall indifferently employ the term isolation for the purpose of designating what in all cases is the same result—namely, a prevention of intercrossing between A and B, where A is the separated portion and B the rest of the species or kind. ”

“ The formation and maintenance of a species, considered as an assemblage of similar organisms, is interpretable in an analogous way. We have already seen that in so far as the members of a species are subject to different sets of incident forces, they are differentiated, or divided into varieties. And here it remains to add that in so far as they are subject to like sets of incident forces, they are integrated, or reduced to, and kept in, the state of a uniform aggregate. ”

“ The extraordinary facts that have been discovered by Professors Steenstrup, Owen, and others, within a few years, respecting what they call alternate generation, or parthenogenesis, have been thought favorable to the hypothesis of development. Among the mollusca, the polyparia, the entozoa, and infusoria, it is found that, in some species, the result of sexual union is the production of a larva without sex, and, therefore, incapable of propagating in the usual way. ”

“ I am profoundly incredulous of so much self-sacrifice, and my incredulity is borne out by all which I have seen during many long years, not in collection boxes, but on the spots where the Scarabæi work. Outside of the cares of maternity—cares in which it almost always shows itself admirable, the Insect—unless, indeed, it lives in society like bees and ants and some others—thinks and cares for nothing but itself. ”

“ Here too the slave species is only represented by workers. These male and female Anergates—a worker of the species has never been known—are both few in number and weak in themselves. When a pair of them (or a fertilised queen) go off to found a new colony, how do they, or how do their few weak descendants, impress a strong fierce species into their service, by whom the nest is built, and every other service performed? ”

“ In truth, from the point of view of the theory of descent, it appears altogether an unimportant question as to whether we give a wider or a narrower signification to allied groups of forms—whether we choose, that is to say, to call them genera or species, varieties or sub-species. The main fact remains undeniable, viz., the common origin of all the species from one ancestral form. ”

“ So long as they interbreed together, the possible divergence is kept within narrow limits, but whenever a variety is produced, the individuals of which have a partiality for interbreeding, and some amount of sterility when crossed with the parent form, the tie that bound it to the central stock is loosened, and the foundation is laid for the formation of a new species. ”

“ Let the mortality of the population of a large country represent the successive extinction of species, and the birth of new individuals, the introduction of new species. While these fluctuations are gradually taking place everywhere, suppose commissioners to be appointed to visit each province of the country in succession, taking an exact account of the number, names, and individual peculiarities of all the inhabitants, and leaving in each district a register containing a record of this information. ”

“ The Distribution of Orders.—When we pass to the larger groups, termed orders, comprising several families, we find comparatively few cases of restriction and many of worldwide distribution; and the families of which they are composed are strictly comparable to the genera of which families are composed, inasmuch as they present examples of overlapping, or conterminous, or isolated areas, though the latter are comparatively rare. Among mammalia the Insectivora offer the best example of an order, several of whose families inhabit areas more or less isolated from the rest ”

“ In view of these considerations, and the new methods of classification, such as grouping genera into families or orders, and these into sub-orders, tribes, sub-tribes, etc., we can readily understand why the great Harvard Professor should have wholly eliminated community of descent from his idea of "species," or hesitated to regard varieties otherwise than as the result of man's agency.
Indeed, the whole question of species, as well as varieties, is likely to undergo material modifications in the future. ”

“ Thus, as I believe, the wonderful fact of two distinctly defined castes of sterile workers existing in the same nest, both widely different from each other and from their parents, has originated. We can see how useful their production may have been to a social community of insects, on the same principle that the division of labour is useful to civilised man. ”

“ In the systematic collection the species should be arranged serially in accordance with the latest catalogue or monograph, and if the collector intends making a complete study of the group, space should be left for the subsequent insertion of species not at present in his possession and also for new species. ”

“ Basing our arguments 264on ill-fitting analogies with the animal and plant world, we may speculate on the effects of intermixture upon the development of new types—as though the mixture that is taking place in America were in any sense, except a sociological one, different from the mixtures that have taken place in Europe for thousands of years; looking for a general degradation, for reversion to remote ancestral types, or towards the evolution of a new ideal type—as fancy or personal inclination may impel us. ”

“ All the higher and more perfectly organised animals are, with but few exceptions, identical with those of France and Germany; while the few species still considered to be peculiar may be accounted for either by an original local distribution, by preservation here owing to favourable insular conditions, or by slight modifications having been caused by these conditions resulting in a local race, sub-species, or species. ”

“ The first requisite is a definition of what constitutes an INSECT.
An Insect is an articulate animal having the body divided into three distinct divisions, viz., the HEAD (Fig. I. A) , the THORAX (B) , and the ABDOMEN (C) . It is furnished with three pairs of legs, and generally has two pairs of wings, and to acquire this structure the creature passes through several changes, termed its metamorphoses. The head exhibits no distinct divisions, but bears the following appendages: the eyes, antennæ, and organs of the mouth, or trophi. ”