207. Advanced Semi-pupa. 208. Pupa.
EARLY STAGES OF THE HUMBLE BEE.]
Still how did the perfect metamorphosis arise? We can only answer this indirectly by pointing to the Panorpa and Caddis flies, with their nearly perfect metamorphosis, though more nearly allied otherwise to those Neuroptera with an incomplete metamorphosis, as the lace-winged fly, than the insects of any other suborder. If, among a group of insects such as the Neuroptera, we find different families with all grades of perfection in metamorphosis, it is possible that larger and higher groups may exist in which these modes of metamorphosis may be fixed and characteristic of each. Had we more s.p.a.ce for the exposition of many known facts, the sceptic might perceive that by observing how arbitrary and dependent on the habits of the insects are the metamorphoses of some groups, the fixed modes of other and more general groups may be seen to be probably due to biological causes, or in other words have been acquired through changes of habits or of the temperature of the seasons and of climates. Many facts crowd upon us, which might serve as ill.u.s.trations and proofs of the position we have taken. For instance, though we have in tropics rainy and dry seasons when, in the latter, insects remain quiescent in the chrysalis state as in the temperate and frigid zones, yet did not the change from the earlier ages of the globe, when the temperature of the earth was nearly the same the world over, to the times of the present distribution of heat and cold in zones, possibly have its influence on the metamorphoses of insects and other animals? It is a fact that the remains of those insects with a complete metamorphosis (the bees, b.u.t.terflies and moths, flies and beetles) abound most in the later deposits, while those with an incomplete metamorphosis are fewer in number and the earliest to appear.
Again, certain groups of insects are not found in the polar regions.
Their absence is evidently due to the adverse climatic conditions of those regions. The development of the same groups is striking in the tropics, where the sum of environing conditions all tend to favor the multiplication of insect forms.
It should be observed that some insects, as the gra.s.shopper, for example, as Muller says, "quit the egg in a form which is distinguished from that of the adult insect almost solely by the want of wings," while the freshly hatched young of the bee, we may add, is farthest from the form of the adult. It is evident that in the young gra.s.shoppers, the metamorphoses have been pa.s.sed through, so to speak, in the egg, while the bee larva is almost embryonic in its build. The helpless young maggot of the wasp, which is fed solely by the parent, may be compared to the human infant, while the l.u.s.ty young gra.s.shopper, which immediately on hatching takes to the gra.s.s or clover field with all the enthusiasm of a duckling to its native pond, may be likened to that young feathered mariner. The lowest animals, as a rule, are at birth most like the adult. So with the earliest known crustacea. The king crabs, and in all probability the primeval trilobites, pa.s.sed through their metamorphoses chiefly in the egg. So in the ancient Nebaliads (Peltocaris, Discinocaris and Ceratiocaris), if we may follow the a.n.a.logy of the recent Nebalia, the young probably closely resembled the adult, while the living crabs and shrimps usually pa.s.s through the most marked metamorphoses. Among the worms, the highest, and perhaps the most recent forms, pa.s.s through the most remarkable metamorphoses.
[Ill.u.s.tration: 209. Jaws of Ant Lion.]
Another puzzle for the evolutionist to solve is how to account for the change from the caterpillar with its powerful jaws, to the b.u.t.terfly with its sucking or haustellate mouth-parts. We shall best approach the solution of this difficult problem by a study of a wide range of facts, but a few of which can be here noticed. The older entomologists divided insects into haustellate or suctorial, and mandibulate or biting insects, the b.u.t.terfly being an example of one, and the beetle serving to ill.u.s.trate the other category. But we shall find in studying the different groups that these are relative and not absolute terms. We find mandibulate insects with enormous jaws, like the Dytiscus, or Chrysopa larva or ant lion, perforated, as in the former, or enclosing, as in the latter two insects, the maxillae (_b_), which slide backward and forward within the hollowed mandibles (_a_, Fig. 209, jaws of the ant lion), along which the blood of their victims flows. They suck the blood, and do not tear the flesh of their prey. The enormous mandibles of the adult Corydalus are too large for use and, as Walsh observed, are converted in the male into simple clasping organs. And to omit a number of instances, in the suctorial Hemiptera or bugs we have different grades of structure in the mouth-parts. In the biting lice (Mallophaga) the mouth is mandibulate; in the Thrips it is mandibulate, the jaws being free, and the maxillae bearing palpi, while the Pediculi are suctorial, and the true bugs are eminently so. But in the bed bug it is easy to see that the beak is made up of the two pairs of jaws, which are simply elongated and adapted for piercing and sucking. Among the so-called haustellate insects the mouth-parts vary so much in different groups, and such different organs separately or combined perform the function of sucking, that the term haustellate loses its significance and even misleads the student. For example, in the house fly the tongue (Fig. 210 _l_, the mandibles, _m_, and maxillae, _mp_, are useless), a fleshy prolongation of the labium or second maxillae, is the sucker, while the mandibles and maxillae are used as lancets by the horse fly (Fig. 211, _m_, mandibles, _mx_, maxillae). The maxillae in the b.u.t.terfly are united to form the sucking tube, while in the bee the end of the labium (Fig.
212) is specially adapted for lapping, not sucking, the nectar of flowers. But even in the b.u.t.terfly, or more especially the moth, there is a good deal of misapprehension about the structure of the so-called "tongue." The mouth-parts of the caterpillar exist in the moth. The mandibles of the caterpillar occur in the head of the moth as two small tubercles (Fig. 213, _m_). They are aborted in the adult. While the maxillae are as a rule greatly developed in the moth, in the caterpillar they are minute and almost useless. The labium or second maxillae, so large in the moth, serves simply as a spinneret in the caterpillar. But we find a great amount of variation in the tongue or sucker of moths, and in the silk moths the maxillae are rudimentary, and there is no tongue, these organs being but little more developed than in the caterpillar. Figure 213, B, shows the minute blade-like maxilla of the magnificent Luna moth, an approximation to the originally blade-like form in beetles and Neuroptera. The maxillae in this insect are minute, rudimentary, and of no service to the creature, which does not take food. In other moths of the same family we have found the maxillae longer, and touching at their tips, though too widely separate at base to form a sucking tube, while in others the maxillae are curved, and meet to form a true tube.
[Ill.u.s.tration: 210. Mouth-parts of the House fly.]
[Ill.u.s.tration: 211. Mouth-parts of Horse fly.]
[Ill.u.s.tration: 212. Head of Humble bee.]
[Ill.u.s.tration: 213. Mouth-parts of Moths.]
In the Cecropia moth it is difficult to trace the rudiments of the maxillae at all, and thus we have in the whole range of the moths, every gradation from the wholly aborted maxillae of the Platysamia Cecropia, to those of Macrosila cluentius of Madagascar, which form a tongue, according to Mr. Wallace, nine and a quarter inches in length, probably to enable their owner to probe the deep nectaries of certain orchids.
These changes in form and size are certainly correlated with important differences in habits, and the evolutionist can as rightly say that the structural changes were induced by use and disuse and change of habits and the environment of the animal, as on the other hand the advocate of special creation claims that the two are simply correlated, and that is all we know about it.
[Ill.u.s.tration: 214. Ichneumon Fly.]
Another set of organs, placed on quite another region of the body, unite to form the sting of the bee, or its equivalent the ovipositor of other hymenopterous insects, such as the Ichneumon fly (Fig. 214), the "saw"
of the saw fly, and the augur of the Cicada. These are all formed on the same plan, arising early in the larval stage as three pairs of little tubercles, which ultimately form long blades, the innermost const.i.tuting the true ovipositor. We have found that one pair of these organs forms the "spring" of the Podura, and that in these insects it is three jointed, and thus is morphologically a pair of legs soldered together at their base. We would venture to regard the ovipositor of insects as probably representing three pairs of abdominal legs, comparable with those of the Myriopods, and even, as we have suggested in another place, the three pairs of jointed spinnerets of spiders. Thus the ovipositor of the bee has a history, and is not apparently a special creation, but a structure gradually developed to subserve the use of a defensive organ.
So the organs of special sense in insects are in most cases simply altered hairs. The hairs themselves are modified epithelial cells. The eyes of insects, simple and compound, are at first simply epithelial cells, modified for a special purpose, and even the egg is but a modified epithelial cell attached to the walls of the ovary, which in turn is morphologically but a gland. Thus Nature deals in simples, and with her units of structure elaborates as her crowning work a temple in which the mind of man, formed in the image of G.o.d, may dwell. Her results are not the less marvellous because we are beginning to dimly trace the process by which they arise. It should not lessen our awe and reverence for Deity, if with minds made to adore, we also essay to trace the movements of His hand in the origin of the forms of life.
Some writers of the evolution school are strenuous in the belief that the evolution hypothesis overthrows the idea of archetypes, and plans of structure. But a true genealogy of animals and plants represents a natural system, and the types of animals, be they four, as Cuvier taught, or five, or more, are recognized by naturalists through the study of dry, hard, anatomical facts. Accepting, then, the type of articulates as founded in nature from the similar modes of development and points of structure perceived between the worms and the crustacea on the one hand, and the worms and insects on the other, have we not a strong genetic bond uniting these three great groups into one grand subkingdom, and can we not in imagination perceive the successive steps by which the Creator, acting through the laws of evolution, has built up the great articulate division of the animal kingdom?
FOOTNOTES:
[Footnote 14: Memoirs of the Peabody Academy of Science, II.
Embryological Studies on Diplax, Perithemis, and the Thysanurus genus Isotoma. Salem, 1871.]
[Footnote 15: Translated in 1859 by Mr. Dallas under the t.i.tle "Facts for Darwin."]
[Footnote 16: "Whether that common stem-form of all the Tracheata [Insects, Myriopods and Spiders] which I have called Protracheata in my "General Morphology" has developed directly from the true Annelides (Coelminthes), or, the next thing to this (_zunachst_), out of Zoea-form Crustacea (Zoepoda), will be hereafter established only through a sufficient knowledge and comparison of the structure and mode of growth of the Tracheata, Crustacea and Annelides. In either case is the root of the Tracheata, as also of the Crustacea, to be sought in the group of the true jointed worms (Annelides, Gephyrea and Rotatoria." He considers the first insect to have appeared after the Silurian period, viz., in the Devonian.]
[Footnote 17: The Zoea is born with eight pairs of jointed appendages belonging to the head, and with no thoracic limbs, while in insects there are but four pairs of cephalic appendages and three pairs of legs.
Correlated with this difference is the entirely different mode of grouping the body segments, the head and thorax being united into one region in the crab, but separate in the insects, the body being as a rule divided into a head, thorax and abdomen, while these regions are much less distinctly marked in the crabs, and liable in the different orders to great variations. The great differences between the Crustacea and insects are noticeable at an early period in the egg.]
[Footnote 18: Considerations on the Trans.m.u.tation of Insects in the Sense of the Theory of Descent. Read before the Imperial Zoological-botanical Society in Vienna, April 3, 1869.]
[Footnote 19: American Naturalist, vol. 3, p. 45, March, 1869.]
[Footnote 20: See Prof. Torell"s discovery of Eophyton Linnaeanum, a supposed land plant allied to the rushes and gra.s.ses of our day, in certain Swedish rocks of Lower Cambrian age. The writer has, through the kindness of Prof. Torell, seen specimens of these plants in the Museum of the Geological Survey at Stockholm. Mr. Murray, of the Canadian Geological Survey, was the first to discover in America (Labrador, Straits of Belle Isle) this same genus of plants. They are described and figured by Mr. Billings, who speaks of them as "slender, cylindrical, straight, reed-like plants," in the "Canadian Naturalist" for August, 1872.
Should the terrestrial nature of these plants be established on farther evidence, then we are warranted in supposing that there were isolated patches of land in the Cambrian or Primordial period, and if there was land there must have been bodies of fresh water, hence there may have been both terrestrial and aquatic insects, possibly of forms like the Podurids, May flies, Perlae, mites and Pauropus of the present day. There was at any rate land in the Upper Silurian period, as Dr. J. W. Dawson describes land plants (Psilophyton) from the Lower Heiderberg Rocks of Gaspe, New Brunswick, corresponding in age with the Ludlow rocks of England.
We might also state in this connection that Dr. Dawson, the eminent fossil botanist of Montreal, concludes from the immense ma.s.ses of carbon in the form of graphite in the Laurentian rocks of Canada, that "the Laurentian period was probably an age of most prolific vegetable growth.
* * * Whether the vegetation of the Laurentian was wholly aquatic or in part terrestrial we have no means of knowing." In 1855, Dr. T. Sterry Hunt a.s.serted "that the presence of iron ores, not less than that of graphite, points to the existence of organic life even during the Laurentian or so-called Azoic period." In 1861 he went farther and stated his belief in "the existence of an abundant vegetation during the Laurentian period." The Eophyton in Labrador occurs above the Trilobite (Paradoxides) beds, while in Sweden they occur below.]
[Footnote 21: In a communication made to the Boston Society of Natural History, Oct. 17, 1870 (see also "American Naturalist" for Feb. and Sept., 1871).]
[Footnote 22: On the Origin of Insects, a paper read before the Linnaean Society of London Nov. 2, 1871, and reported in abstract in "Nature,"
Nov. 9, 1871.]
[Footnote 23: This reminds us (though Ganin does not mention it) of the development of the embryo of Julus, the Thousand legs, which, according to Newport, hatches the 25th day after the egg is laid. At this period the embryo is partially organized, having faint traces of segments, and is still enveloped in its embryonal membranes and retains its connection with the sh.e.l.l. In this condition it remains for seventeen days, when it throws off its embryonal membrane, and becomes detached from the sh.e.l.l.]
[Footnote 24: It is a suggestive fact that these deciduous forms give way through histolysis to true larval forms, just as in some flies (Musca vomitoria) the true larval form goes under, and the adult form is built up from the imaginal disks of the larva. In an a.n.a.logous manner the deciduous, pluteus-condition of the young Echinoderm perishes and is absorbed by the growing body of the permanent adult stage. This deciduous stage of the ichneumon may accordingly be termed the prelarval stage. Now as we find insects with and without this prelarval stage, and in the radiates quite different degrees of metamorphoses, the inquiry arises how far these differences are correlated with, and consequently dependent upon, the physical surroundings of these animals in the free swimming condition. Merely to point out the differences in the mode of development of animals is an interesting matter, and one could do worse things, but the philosophical naturalist cannot rest here. He must seek how these differences were brought about.]
[Footnote 25: Leuckart, in his great work, "Die Menschlichen Parasiten,"
p. 700, after the a.n.a.logy of Hirudo, which develops a primitive streak late in larval life, ventures to consider the first indications of the germ of Nemertes in its larval, Pilidium form as a primitive streak. He also suggests that the development of the later larval forms of the Echinoderms is the same in kind.
Moreover, nearly twenty years ago (1854) Zaddach, a German naturalist, contended that the worms are closely allied in their mode of development to the insects and crustaceans. He compares the mode of development of a leech (Clepsine) and certain bristle-bearing worms (Saenuris, Lumbricatus and Uaxes); and we may now from Kowalensky"s researches (1871) add the common earth worm (Lumbricus), in which there is no such metamorphosis as in the sea Nereids, to that of insects; the mode of formation of the primitive band in the leeches and earth worms being much like that of insects. This confirms the view of Leuckart and Ganin, who both seem to have overlooked Zaddach"s remarks. Moreover, the rings of the harder bodied worms, as Zaddach says, contain chitine, as in the insects.
Zaddach also enters into farther details, which in his opinion ally the worms nearer to the insects than many naturalists at his time were disposed to allow. The singular Echinoderes has some remarkable Arthropod characters.]
[Footnote 26: Vergleichende Anatomie, 2te Auflage, 1870, p. 437. I should, however, here add that I am told by Mr. Putnam that some fishes which have no swim-bladder, are surface-swimmers, and _vice versa_.]
[Footnote 27: Reported In "Nature" for Nov. 9, 1871.]
[Footnote 28: The Embryology of Chrysopa, and its bearings on the Cla.s.sification of the Neuroptera, "American Naturalist," vol. v. Sept., 1871.]
[Footnote 29: "It is my opinion that the "incomplete metamorphosis" of the Orthoptera is the primitive one, _inherited_ from the original parents of all insects, and the "complete metamorphosis" of the Coleoptera, Diptera, etc., a subsequently acquired one." _Fuer Darwin_, English Trans., p. 121.]
CHAPTER XIV.
INSECT CALENDAR.
In this calendar I propose to especially notice the injurious insects.
References to the times of their appearance must be necessarily vague, and apply only, in a very general way, to the Northern States. Insects appear in Texas about six weeks earlier than in Virginia, in the Middle States six weeks earlier than in northern New England and the North-western States, and in New England about six weeks earlier than in Labrador. The time of the appearance of insects corresponds to the time of the flowering or leafing out of certain trees and herbs; for instance, the larvae of the American Tent caterpillar and of the Canker worm hatch just as the apple tree begins to leaf out; a little later the Plant lice appear, to feast on the tender leaves; and when, during the first week in June, our forests and orchards are fully leafed out, hosts of insects are marshalled to ravage and devour their foliage.
_The Insects of Early Spring._
In April the gardener should sc.r.a.pe and wash thoroughly all his fruit trees, so as to rub off the eggs of the bark lice which hatch out early in May. Many injurious caterpillars and insects of all kinds winter under loose pieces of bark, or under matting and straw at the base of the trees. Search should also be made for the eggs of the Canker worm and the American Tent caterpillar, which last are laid in bunches half an inch long on the terminal shoots of many of our fruit trees. A little labor spent in this way will save many dollars" worth of fruit. The "castings" of the Apple Tree Borer (Saperda bivittata) should be looked for at the base of the tree, and its ravages be promptly arrested. Its presence can also be detected, it is said, by the dark appearance of the bark, where the grub is at work: cut in and pull out the young grub. It is the best time of the year to catch and kill this pest. Cylindrical bark borers, which are little round, black, weevil-like beetles, often causing "fire-blight" in pears, etc., are now flying about fruit trees to lay their eggs; and many other weevils and boring beetles, especially the Pea weevil (Bruchus pisi, Fig. 215), the Pine weevil (p.i.s.sodes strobi, Fig. 216), and Hylobius pales and Hylurgus terebrans, also infesting the pine, now abound, and the collector can obtain many specimens not met with at other times.
[Ill.u.s.tration: 215. Pea Weevil and Maggot.]