Insects

These are imperfect animals:

• undergoing transformations of form with 2 eyes and 2 antennae on the head, 6 limbs, and 2 trachea extending throughout the entire body.
• do not have arteries, no veins
• breathe by air through a trachea which are not limited
• born in a state less perfect than that in which they reproduce, consequently undergo metamorphosis.

They come after the arachnids.

Once they reach their perfect condition, all the insects, without exception, have 6 articulated limbs, 2 antennae and 2 eyes on the head, and most of them then have wings.

According to the order we are following, the insects of necessity take up the tenth rank in the animal kingdom.

For they are inferior in improvements to their organic structure to the arachnids, because they are not, like the latter, born in their perfect condition and they reproduce only once during the course of their lives.

Particularly among the insects we begin to notice that the organs essential to maintain life are distributed almost equally and most of them are situated throughout the extent of the body, rather than being isolated in particular places, as was the case in the most improved animals.

This consideration gradually loses its exceptions and becomes more and more striking in the animals in the later classes.

Nowhere, up to this point, is the general degradation in organic structure more manifest than in the insects, where that structure is inferior in improvements to that of the animals in all the preceding classes.

This degradation even shows up between the different orders which naturally divide the insects. For those in the three first orders (Coleoptera, Orthoptera, and Neuroptera) have mandibles and jaws in their mouths.

Those of the fourth order (Hymenoptera) begin to possess a sort of proboscis; finally those of the four last orders (Lepidopteres, Hemiptera, Diptera and Aptera) really have only a proboscis.

Paired jaws do not turn up anywhere in the animal kingdom after the insects of the three first orders. With respect to wings, the insects of the six first orders have four of them, of which all or two alone serve for flight. Those of the seventh and eighth orders have only two wings, or their wings are aborted. The larvae of insects of the two final orders do have limbs and resemble worms.

It appears that insects are the last animals which display a clearly distinct sexual reproduction and which are truly oviparous.

Finally, we will see that the insects are infinitely remarkable for the details concerning what has been called their industry but that this alleged industry is not at all the product of any thinking, that is, of any combination of ideas on their part.

Observation

Just as the fish, among the vertebrates, display in their general shape and in the anomalies relative to the progression in complexity of organic structure, the results of the influence of their environmental habitat, so the insects, among the invertebrates, display in their form, organic structure, and transformations, the clear result of the influence of the open air in which they live and up into which most of them leap and habitually stay, like the birds.

If the insects had had a lung, if they had been capable of inflating themselves with air, and if the air which reaches all parts of their body had been able to rarefy itself there, like the air which goes into the bodies of birds, their hairs would have been changed, no doubt, into feathers.

Finally, if, among the invertebrate animals, it is astonishing to find so few affinities between the insects which undergo singular metamorphoses and the invertebrate animals of the other classes, one should draw attention to the fact that these are the only animals without vertebrae who leap up into the air and carry out progressive movements there. Then one will sense that quite special circumstances and habits must have produced results which are just as special.

The insects are close only to the arachnids in their interrelationships. And, in fact, both of them are, in general, the only animals without vertebrae which live in the air. But no spider has the ability to fly, and no arachnid likewise undergoes transformation. In dealing with influences of habits, I will show that these animals, because they were accustomed to stay on parts of the surface of the earth and to live in hidden places, must have lost some of the ability of insects and to acquire characteristics which clearly distinguish them from insects.

The Destruction of Several Organs Essential to the More Improved Animals After the insects, it appears that there is quite a considerable gap in the series, which animals we have not observed remain to fill in. For in this position in the series, several organs essential to more improved animals suddenly are missing and are really done away with, because we do not find them again in the classes which remain for us to review.

The Disappearance of the Nervous System Here the nervous system (the nerves and their central connection) effectively disappears completely and does not appear any more in any of the animals of the classes which follow.

In the most improved animals, this system consists of a brain which appears to serve to carry out of acts of intelligence, at the base of which is located the chamber of sensations, from which the nerves leave, as well as a dorsal spinal chord which sends other nerves out to the various parts.

In the vertebrates, the brain successively diminishes, and as its volume gets smaller, the spinal column becomes larger and seems to take its place.

In the mollusks, the first class of invertebrates, the brain still exists, but it does not have a spinal chord or longitudinal marrow with ganglia. Since the ganglia are rare, the nerves do not appear knotty.

Finally, in the five classes which follow, the nervous system, in its last stage, is reduced to a very small brain, hardly a trace, and a longitudinal marrow which sends nerves to the parts. From that point on there is no isolated chamber for sensations, but a multitude of small places spread throughout the full length of the animal.

Thus, in the insects the important system of feeling ends, that system which, at a particular stage of its development, gives rise to ideas, which in its highest perfection can produce all intelligent acts, and which, finally, is the source where muscular action gets its power and without which sexual reproduction apparently cannot exist.

Disappearance of the Sexual Organs

Traces of sexual reproduction disappear completely.

Of the 2 classes which follow, species with types of ovaries in oviform corpuscles which are taken for eggs.

But I consider these alleged eggs, which can produce without prior fertilization as buds or internal gemmules. They create the link between internal gemmiparous reproduction and oviparous sexual reproduction.

The inclination of human beings for their own habits is so great that they persist, even against the evidence, to look at things always in the same manner.

This is why botanists, accustomed to observe the sexual organs of a large number of plants, want all plants, without exception, to have similar organs.

Consequently, several of them have made every imaginable effort, with respect to the plants cryptogames or agames, to discover stamens and pistils. And they have preferred to attribute to the plants arbitrarily and without proof functions to those parts whose use they did not know rather than to recognize that nature knows how to reach the same goal by different means.

We were persuaded that every reproductive body is a seed or an egg, that is, a body which, in order to be reproductive, needs to undergo the influence of sexual fertilization.

This made Linnaeus state: Omne vivum ex ovo [All living things are from the egg].

But plants and animals which regenerate themselves solely by bodies which are neither seed nor eggs.

• And so they do not need sexual fertilization.

Thus, these bodies are shaped differently and develop in a different manner.

Every reproductive corpuscle, whether plant or animal, which, without breaking through any enclosing material, grows longer and larger and become a plant or animal similar to the one which it came from is neither a seed nor an egg.

It does not undergo any fertilization or hatch after having started to grow.

Its formation has not required any sexual impregnation.

Thus it does not contain an embryo enclosed in layers which must be broken through, as in the seed or the egg.

Now, follow attentively the developments of the reproductive corpuscles of algae, fungi, and so on, and you will see that these corpuscles only grow longer and larger so as to take on imperceptibly the form of the plant from which they issued forth.

They do no break through any enclosing material, as does the embryo of the seed or the one that contains the egg.

Similarly, if you follow the gemma or bud of a polyp, like the hydra, you will be convinced that this reproductive body only grows longer and larger. It does not break through any exterior covering that it does not hatch like a chicken or a silk worm coming from an egg.

Thus, all reproduction does not happen by sexual fertilization.

Where there is no sexual fertilization, there is no true sexual organ.

The 4 classes after the insects do not follow any organ of fertilization.

At this point in the animal chain, sexual reproduction ceases.

Disappearance of the Eyes

The eyes started to be absent in a section of the:

• mollusks
• cirrhipedes
• most of the annelids.

They are found again in a very imperfect condition in:

• crustaceans
• arachnids
• insects

They do not reappear after the insects in any animal.

At this point also, the head totally ceases to exist.

The bulge in the forward extremity of some worms, like the Taenia, is caused by the arrangement of their suckers.

• It is neither the seat of a brain nor of organs of hearing, sight, etc.
• All these organs are lacking in the animals of the classes which follow.
• The swelling cannot be considered a true head.

At this stage of the animal scale, the degradation in organic structure becomes extremely rapid.

It makes one look ahead to the greatest simplification in the organic structure of animals.