packets of pollen. By the time the nectar is exhausted the gland has become adherent to the bee's head, and as it (the head) is withdrawn, the two pollen masses are extracted from their pockets, and now stand off in front like a pair of horns. The bee, most likely, flies to another plant of the same species, or still more probably to another flower of the same plant. Suppose the stigmatic surface of this species of plant be broad, or possibly separated almost into two parts; we will find the packets have slowly but surely diverged so as to be the exact width of that surface. Suppose on the other hand, the stigma be a narrow one, we shall find that the packets have come close together. In either case when the bee's head bobs down into the next flower, it will almost certainly happen that these same pollen masses will be left sticking on the stigma when the bee leaves, or at least part of the pollen will be left. These masses of pollen have long since been frequently observed on the bee's head, but, until quite lately, no meaning had been attached to it. Some entomologists, I believe, have even been guilty of describing these as natural appendages to the bee's head. So manifest are these adaptations for the purpose of cross fertilization among Orchids, that we may be well nigh sure some great purpose is to be subserved. Perhaps it would not be too much to say, that but for insect agency many Orchids would become extinct. There are not wanting those who even affirm the insect shape assumed by some Orchidaceous flowers, has no less purpose than to serve as a decoy, and thus tempt the bee or butterfly to alight upon them and accomplish the work of fertilization. Those wishing to be apprized of the mode of fertilization, as it occurs in our American plants, will find some admirable articles from the pen of Prof. Asa Gray, in Silliman's Journal

for 1862. Robert Brown long since called attention to insect agency, in the fertilization of the Milkweed family. Almost any summer day we may repeat his observations for ourselves. So adhesive are the glands of the Asclepias obtusifolia (Wavey-leaved Milkweed), that we often find honey bees unable either to withdraw the packets, or loose their feet from the gland, and thus they become prisoners for life.

There exists yet another class of dimorphic flowers, in which we find the large and more conspicuous flowers less fertile than those of the other form, which are arrested in their development, and are fertilized in the bud. Hugo van Mohl has of late called especial attention to them. Such flowers have been happily termed precociously fertilized. Mohl concludes, after close examination of Viola, Oxalis, Specularia and Impatiens, that nature is here specially solicitous to secure close breeding, or that each flower shall be fertilized by its own pollen. He calls attention also to the fact, that in the large anthers of the smaller form of Oxalis acetosella, not more than two dozen pollen grains are found, while in the anthers of the larger form they are much more numerous. In the smaller form, however, the few grains are made more potent, and the exercise of their function is secured, by being placed in contact with the stigma. It results, however, that our list of closely fertilized plants is becoming smaller, under the repeated observations of accurate investigators, and that, what was supposed to be a special adaptation to secure close fertilization, is, after all, but a more nicely conceived method of obtaining an opposite result. For example, we were formerly taught that the interior petals of Corydalis clasped the anthers and stigma of the flower in so tight an embrace that outside fertilization

was a thing not to be thought of. Dr. Hildebrand informs us however, that though the stigma of Corydalis cava be completely dusted over with pollen from the same flower, yet no seed will set if insects be excluded from carrying pollen from flower to flower. This fact is, as will be observed, another illustration of Mr. Darwin's law of prepotency of pollen taken from one flower, and applied to another. Professor Gray also calls attention to the "effectual activity of so large an insect as the bumble-bee in fertilizing our Corydalis aurea" (Golden Corydalis).

Just now we can point to but one instance in which a plant of high order is found to produce perfect embryos, without the ovules having been previously fertilized according to the known method. In the Kew Gardens, near London, has been kept for many years a plant of the Spurge family, which furnishes this one example. Dr. Hooker writes to Humboldt concerning it, as follows: "Our Cœlebogyne still flowers with my father at Kew, as well as in the Garden of the Horticultural Society. It ripens its seeds regularly. I have repeatedly examined it with care, but have never been able to discover a penetration of pollen utricles into the stigma, nor any traces of their presence in the latter or in the style." This plant belongs to the old Linnæan class Diœcia. It is unisexual, and as there exists only (so far as known) the female plant in England, it is difficult to conceive how the fertilization is accomplished, unless through the agency of concealed anthers. Though diligent search has been made time and again for the anthers, they do not seem to have been found. We may still fairly hesitate before accepting this as an example of parthenogenesis, or virgin fertility.

INSECTS AND THEIR ALLIES.

BY A. S. PACKARD, JR., M. D.

73

That branch of the Animal Kingdom known as the ARTICULATA, is so called from having the body composed of rings or segments, like short cylinders, which are placed successively one behind the other. Cuvier selected this term because he saw that the plan of their entire organization, the essential features which separate them Fig. 1. from all other animals, lay in the idea of articulation, the apparent joining together of distinct segments along the line of the body. If we observe carefully the body of the Worm, we shall see that it consists of a long cylindrical sac, which at regular intervals is folded in upon itself, thus giving a ringed, annulated or articulated appearance to the body. In the Crustacea (Crabs, Lobsters, etc.) and in the Insects, from the deposition of an earthy salt, called Wormchitine, the walls of the body become so hardened, larva of that when the animal is dead and dry, it readily Thereva? breaks into numerous very perfect rings.

like

a Fly,

Though this branch contains a far greater number of species than any other of the animal kingdom, their myriad forms can all be reduced to a simple, ideal, typical figure; that of a long slender cylinder divided into numerous segments, as in Fig. 1, representing the larva of a Fly. It is by the unequal development and the various modes of grouping them, as well as the differences in the number of the rings themselves, and also in the changes of form of their appendages, i. e., the feet, jaws, antennæ and wings, that the various forms of Articulates are produced.

In all Articulates the long, tubular, alimentary canal occupies the centre of the body; above it lies the "heart,"

or dorsal vessel, and below, upon the under side, rests the nervous system. The breathing apparatus, or "lungs,' in Worms consists of simple filaments, placed on the front of the head; or of gill-like processes, as in the Crustacea, which form simple expansions of the legs; or, as in the Insects, of delicate tubes (trachea), which ramify throughout the whole interior of the animal, and connect with breathing pores (stigmata) in the sides of the body. They do not breathe through the mouth as do the higher animals. The trachea and blood-vessels follow closely the same course, so that the aëration of the blood goes on, apparently, over the whole interior of the body, not being confined to a single region, as in the lungs of the vertebrate animals.

Thus it is by observing the general form of the bodywalls, and the situation of the different anatomical systems, both in relation to themselves and the walls of the body, or crust, which surrounds and protects the more delicate organs within, that we are able to find satisfactory characters for isolating, in our definitions, the articulates from all other animals.

Fig. 2.

We shall perceive more clearly the differences between the three classes of articulates, or jointed animals, by examining their young stages, from the time of their exclusion from the egg, until they pass into mature life. A more carebella, soon ful study of this period than we are able to enter

Young Tere

after leaving

the egg.

A. AGASSIZ, upon at present, would show us how much alike the young of all articulates are at first, and how soon they begin to differ, and assume the shape of their class.

Most Worms, after leaving the egg, are at first like some infusoria, being little sac-like animalcules, often ciliated over nearly the entire surface of the infinitesimal