Class 1: Infusorians

These do not have any vertebral column and consequently have no skeleton.

Those which have points of support for the movement of parts have them under their teguments.

They lack a spinal chord and present a great diversity in the complexity of their organic structure.

Stage 1

No nerves, no longitudinal ganglionic chord, no vessels for circulation, no respiratory organs; no other special interior organ except for digestion.

Class 1: The Infusorians

These fissiparous animals:

• are amorphous, with gelatinous bodies, transparent, homogeneous, contractile and microscopic
• have no radiating tentacles; no rotary appendages; no special organ in the interior, not even for digestion.

Observations

These are:

• the most imperfect
• the simplest in organic structure
• have the fewest capacities

They have no ability to feel.

Infinitely small, gelatinous, transparent, contractile, almost homogeneous, and incapable of having any special organ because of the excessively weak consistency of their parts.

The infusorians are really only the rudiments of animal life.

These frail animals are the only ones which nourish themselves by absorption and not by digestion.

In this matter, they resemble the plants which:

• live only by absorption
• organic movements operate only through external stimuli

But the infusorians are irritable and contractile.

They go through sudden movements which they can repeat several times in a row.

This classifies them as animals instead of plants.

Table of Infusorians

Order 1: Naked Infusorians

They lack external appendages

Monads Volvox Proteus Vibrio

Bursaria Colpoda

Order 2: Infusorians with Appendages

They have projecting parts, like hairs, types of horns or a tail

Cercaria Trichocerca Trichoda

Remarks. The monad, and especially the one which is called Monas termo, is the most imperfect and simplest of known animals, because its body, which is extremely small, displays only a gelatinous and transparent point, but it is contractile. This animal therefore must be considered the one at which the series of animals, organized according to nature, begins.