Cl. 1. Echinoderms.
Cl. 2. Intestinal Worms.
Cl. 3. Acalephæ.
Cl. 4. Polypi.
Cl. 5. Infusoria.
But though Cuvier emancipated himself from the conception of a serial progression throughout the Animal Kingdom, sundry of his contemporaries and successors remained fettered by the old error. Less regardful of the differently-combined sets of attributes distinguishing the different sub-kingdoms, and swayed by the belief in a progressive development which was erroneously supposed to imply a linear arrangement of animals, they persisted in thrusting organic forms into a quite unnatural order. The following classification of Lamarck illustrates this.
| INVERTEBRATA. | ||
| I. APATHETIC ANIMALS. Cl. 1. Infusoria Cl. 2. Polypi. Cl. 3. Radiaria. Cl. 4. Tunicata. Cl. 5. Vermes. |  | Do not feel, and move only by their excited irritability. No brain, no elongated medullary mass; no senses; forms varied; rarely articulations. |
| II. SENSITIVE ANIMALS. Cl. 7. Arachnids. Cl. 8. Crustacea. Cl. 9. Annelids. Cl. 10. Cirripeds. Cl. 11. Conchifera. Cl. 12. Mollusks. |  | Feel, but obtain from their sensations only perceptions of objects, a sort of simple ideas, which they are unable to combine to obtain complex ones. No vertebral column; a brain and mostly an elongated medullary mass; some distinct senses; muscles attached under the skin; form symmetrical, the parts being in pairs. |
| VERTEBRATA. | ||
| III. INTELLIGENT ANIMALS. Cl. 13. Fishes. Cl. 14. Reptiles. Cl. 15. Birds. Cl. 16. Mammalia. |  | Feel; acquire preservable ideas; perform with them operations by which they obtain others; are intelligent in different degrees. A vertebral column; a brain and a spinal marrow; distinct senses; the muscles attached to the internal skeleton; form symmetrical, the parts being in pairs. |
Passing over sundry classifications in which the serial arrangement dictated by the notion of ascending complexity, is variously modified by the recognition of conspicuous anatomical facts, we come to classifications which recognize another order of facts—those of development. The embryological inquiries of Von Baer led him to arrange animals as follows:—
III. Peripheric Type. (Radiata.) Evolutio radiata. The development proceeds from a centre, producing identical parts in a radiating order.
III. Massive Type. (Mollusca.) Evolutio contorta. The development produces identical parts curved around a conical or other space.