Yersin, by cutting through the commissure in different places, and thus isolating the ganglia of the nervous cord of Gryllus campestris, arrived at the following results:—
1. The section of a nerve near its origin rendered the organ supplied by this nerve incapable of performing its functions.
2. If the connectives between two ganglia, i.e. the second and third thoracic ganglia, are cut through, the fore as well as hinder parts of the body retain their power of motion and sensation; but a stimulus applied to the anterior part of the body does not pass to the hinder portion.
3. Insects with an incomplete metamorphosis after section of the connectives are not in every case unable to moult and to farther develop.
4. If only one of the two connectives be cut through, the appendages of the side cut through which take their origin between the place injured and the hinder end of the body, often lose sensation and freedom of motion, or the power of coördination of movements becomes irregular. Sometimes this is shown by an unsteadiness in the gait, so that the insect walks around in a circle; after a while these irregularities cease, and the movements of the limbs on the injured side are only slightly restrained. By a section of both connectives in any one place the power of coördination of movements is not injured.
5. The section of the connectives appear to have no influence on nutrition, but affects reproduction, the attempt at fertilization on the part of the male producing no result, and the impregnated female laying no eggs.
6. Injury to the brain, or to the subœsophageal, or one of the thoracic ganglia, is followed by a momentary enfeeblement of the ganglion affected. Afterwards there results a convulsive trembling, which either pervades the whole body or only the appendages innervated by the injured ganglion.
7. As a result of an injury to the brain there is such a lack of steadiness in the movements that the insect walks or flies in a circle; for instance, a fly or dragon-fly thus injured in flying describes a circle or spiral. Steiner, in making this experiment, observed that the insect circled on its uninjured side. The brain is thus a motor centre.
8. By injuring a thoracic ganglion, one or all the organs which receive nerves from the ganglion are momentarily weakened. Afterwards the functions become restored. Sometimes, however, the insect walks in a circle. Faivre observed that after the destruction of the metathoracic ganglion of Dyticus marginalis the hind wings and hind legs were partially paralyzed (Kolbe, ex Yersin).