THE CENTRAL NERVOUS SYSTEM IN TERATOPHTHALMIC AND TERATOMORPHIC FORMS OF PLANARIA DOROTOCEPHALA

Abstract

1. The teratophthalmic and teratomorphic forms of Planaria dorotocephala can be produced experimentally by decreasing the rate of the dynamic processes in the isolated pieces below a certain variable level which is necessary for the production of normal forms.2. In these forms the cephalic region of the nervous system differs more or less widely from that of normal animals. The two ganglionic masses are always less completely separated than in the normal animals and often only a single ganglion develops. In the teratomorphic forms the ganglia are more abnormal than in the teratophalmic forms.3. In the normal animals the cephalic ganglia extend a considerable distance anterior to the eyes and the two separate nerve cords arise near the level of the auricles. In the teratophthalmic forms with partially fused eyes the eyes lie nearer the anterior end of the ganglia and the right and left portions are not separated at the level of the auricles. The eyes of the teratomorphic forms are situated at the extreme anterior end of the ganglionic mass.4. The abnormal structure of the nervous system in the teratophthalmic and teratomorphic forms continues posteriorly through the regenerated anterior end to the level of the old tissue and even the nerve cords in the old tissue may be more or less different from the normal. In some teratomorphic forms the regenerated nervous tissue apparently begins to break up into separate nerves a short distance posterior to the eyes, but resumes the form of two nerve cords in the old tissue.5. In the normal animal the optic pigment cups open laterally and the same is true for the teratophthalmic forms with partially fused eyes. In the teratomorphic forms the cup opens anteriorly or antero-ventrally and in some cases more or less to one side. The single median eye may be connected by two nerves with right or left portions of the ganglionic mass, or by a single nerve with either one, or the optic nerve may arise from the median region of the ganglion. The eyes are also farther from the dorsal surface in the teratomorphic than in the normal forms and are sometimes more or less completely imbedded in the ganglionic mass.