The Present Classification of Animals
Table of Contents
Since the purpose and the principles, whether of the general distribution of living beings or of their classification, have not been noticed when we concerned ourselves with these matters, the works of naturalists suffered for a long time from this imperfection of our ideas.
The natural sciences were like all the others which we busied ourselves with for a long time before thinking about the principles which must form the basis of the science and govern the work which goes on in it.
Instead of subjecting the classification necessary in each kingdom of living creatures to a distribution which nothing should interfere with, we thought only of classifying objects conveniently and in this way of subjecting their distribution to arbitrariness.
For example, since the connections between the large groups were very difficult to grasp among the plants, for a long time in botany we used artificial systems.
They made convenient classifications easy to create, based on arbitrary principles. And each author made up new ones according to his fancy. Thus the distribution we need to establish among the plants, the one which, in a word, belongs to the natural method, was then always sacrificed.
Only since we have understood the importance of the parts concerned with the fruit, and above all the preeminence which certain of those parts must have over the others, has the general distribution of plants started to progress towards perfection.
Since the case is not the same so far as animals are concerned, the general connections which characterize the large groups are, among themselves, a great deal easier to perceive. Also several of these groups have been recognized since the time when we first began to cultivate natural history.
Aristotle divided the animals in 2 classes.
| Animals with Blood | Animals without Blood |
|---|---|
| Viviparous quadrupeds | Mollusks |
| Oviparous quadrupeds | Crustaceans |
| Fish | Testaceans |
| Birds | Insects |
This was good enough. But the characteristic used by Aristotle was poor.
He called blood to the principal red fluid in animals.
Assuming that since all the animals which belong to his second class possessed only white or off white fluids, he therefore considered that they lacked blood.
People have generally followed this false direction with regard to the distribution of animals.
- This has clearly held back our knowledge concerning the nature’s march.
Modern naturalists believed that they were perfecting Aristotle’s distinction when they gave to the animals of his first division the name red-blooded animals and to those of the second division the name white-blooded animals.
We are sufficiently aware now how much this characteristic is defective, since there are invertebrate animals with red blood (many annelids).
I think the fluids essential to animals cease to be blood as soon as they no longer circulate in arterial and venous vessels.
These fluids are then so degraded, so lacking in complexity or so imperfect in the combination of their principles, that we were wrong to link their nature to that of fluids which undergo a true circulation.
Besides, attributing blood to a radiate or to a polyp means as much as attributing blood to a plant.
To remove all ambiguity or the use of any hypothetical consideration, in my first course of study which I carried out in the Museum, in the spring of 1794, I divided all animals into 2:
- Animals with backbones
- Animals without backbones
The vertebral column indicates, in the animals which have it, the possession of a skeleton more or less perfect and of a structural plan relative to it.*
Superphysics Note
The lack of a vertebral column in the other animals not only clearly distinguishes them from the first ones, but announces that the structural plans on which they have been developed were all very different from those of the vertebrate animals.
From Aristotle up to Linnaeus, nothing very noteworthy has appeared on the general distribution of animals.
But in the last century, some naturalists of exceeding merit made a large number of particular observations concerning animals, mainly on a number of animals without vertebrae.
Some revealed their anatomy with more or less detail; others provided an exact and detailed history of the changes in and the habits of a large number of these animals.
As a result of their valuable observations, we have come to understand many facts of the highest importance.