3078. Their body itself will only be a tegumentary body, with the organs subordinated to the integument, namely, the viscera. They are therefore devoid of a true tongue, of a nose, and of ears and eyes consummated after the fashion of these organs in man; they are devoid of an osseous, muscular, and myelonal (spinal chord) system, and therefore of the nose "in toto," as being the anterior extremity of the myelon.
3079. Such are what have been called the Invertebrate animals, which are consequently, in accordance with their physiological signification, Splanchnic or Tegumentary animals.
3080. The tongue exhibits for the first time in Fishes a resemblance to the human structure, while their nose, ears, and eyes have not yet attained the latter grade of perfection. To the nose are wanting the posterior nasal foramina, to the ears the external auditory meatus, to the eyes the palpebræ and power of motion.
3081. In the Reptiles the nose opens for the first time into the mouth, and serves for the thorough passage of air. It is thus developed as in Man, while to the ears the external auditory meatus and cochlea are wanting, the eyes being barely endowed with lids and motion.
3082. In Birds, for the first time, the external auditory meatus, as well as the cochlea, is exhibited in its perfection, while the eyes are scarcely gifted with motion, and have only the inferior lid perfect; the tongue and nose, with the limbs also, have again become retrograde in character.
3083. For the first time, in the Mammalia, the eyes are moveable and covered with two perfect lids, without the other organs of sense having suffered degradation through this completion of the eyes.
3084. Thus in respect to the Senses there are only 5 animal divisions of equal value or worth. They should properly be called classes; but, as the lowest division, from comprising within itself the viscera or the vegetative systems, is very rich in contents; were we to call these divisions classes, many inequalities in rank, and hence also in the number of the orders and families, would originate—
| 1. Dermatozoa | Invertebrata. |
| 2. Glossozoa | Pisces. |
| 3. Rhinozoa | Reptilia. |
| 4. Otozoa | Aves. |
| 5. Ophthalmozoa | Mammalia. |
3085. Now, with the sense of feeling, or the integument, the sexual system is associated or conjoined, and that indeed as the first or lowest development of the tegumentary system. Nevertheless, the sexual system divides into two groups, into the sexual organs, which are impressed with a true sensorial signification, and into their product, or the sexual juices, and the ovum or fœtus. With these two divisions the development of the integument proceeds "pari passu."
In the ovum the tegument and its contents are not as yet separated. Both consist of a transparent mucous or gelatinous mass, as is exemplified by the vitellus and albumen; such is the case also in the Infusoria, Polyps, and Acalephæ or Sea-nettles.