3307. The animal systems are for the first time slightly separated from each other. Bone, muscle, and nerve are rather a gelatinous mass, which only bids fair for becoming something higher; on this account the bones are frequently but soft cartilages or tendons, the muscle composed of white fibres like those upon the intestine or vessels, the nerve thick, oleaginous, and soft in texture, while the brain is in its constituent parts hardly comparable with that of the Thricozoa.
3308. The muscles of Fishes are not yet perfect in character, since they are devoid of individualization and red colour, and their fibres run mostly parallel with each other without uniting into tendons. Their muscular body is a muscular wall.
3309. The Fishes, ranking upon the first stage of the Sarcozoa, repeat the same stage of the preceding circle, and thus the Infusoria, Mussels, and Worms; or the stomach, veins, and branchial rete or network; furthermore, the vitellus, ovary, and skin, which systems must in them accordingly predominate.
Pelvis.
3310. In Fishes the pelvic organs, sexual parts, and tail predominate. The tail, as being an appurtenance of the pelvis, is larger and stronger than in other animals. It mostly makes up the largest part of the body, and is, properly speaking, its only motor organ.
3311. The sexual parts have still the form of the intestine, and occupy the greatest part of the abdomen. The ovaria are two sacs, like two Infusoria, in whose parietes granules are developed; even the testes are only two such sacs or seminal vesicles wherein the "milt" is contained. Fishes may be termed anorchitic, or animals devoid of testes.
The ova are small, consisting of spawn or roe without shell, but they separate into albumen and vitellus.
3312. External sexual parts are not present. Everything usually opens into a cloaca, which is thus here a true pharyngeal cavity.
3313. With the perfected formation of the head, the animal, so to speak, undergoes a sudden and entire change, and the sexual parts are developed with all their accessory organs, such as the sexual lung. Kidneys are present and mostly an urinary cyst. The kidneys are indeed still so amorphous and soft, that they more resemble coagulated blood than an organ, yet meanwhile agree in this respect with the 'milt' and branchial substance.
Abdomen.