The dynamics of living matter . dynamicsofliving1906loeb Year: 1906 214 DYNAMICS OF LIVING MATTER the experimenter has it entirely in his power to determine whether the Crustacean shall regenerate an eye in the place of the eye which has been cut off, or an antenna. It depends upon the fact whether or not in the operation the optic ganglion is removed with the eye. If the optic ganglion is removed with the eye, an antenna is regenerated in the place of the eye. If the optic ganglion is left intact, a new eye is formed. These experiments were carried on successfully in Palaemon, Palaemonetes,
The dynamics of living matter . dynamicsofliving1906loeb Year: 1906 214 DYNAMICS OF LIVING MATTER the experimenter has it entirely in his power to determine whether the Crustacean shall regenerate an eye in the place of the eye which has been cut off, or an antenna. It depends upon the fact whether or not in the operation the optic ganglion is removed with the eye. If the optic ganglion is removed with the eye, an antenna is regenerated in the place of the eye. If the optic ganglion is left intact, a new eye is formed. These experiments were carried on successfully in Palaemon, Palaemonetes, Sicyonia, Palinurus, and other Crustaceans. Herbst says that the optic ganglion exercises a 'formative stimulus' upon the hypodermic cells of the wound. It is certain that an explanation of the role of the ganglion can only be given in physical or chemical terms; that as long as this is not possible we possess no explanation. Morgan has made a somewhat similar observation on earthworms, in which he found that a new head is only possible at the anterior cut end of the nerve cord.* The following case may be mentioned by way of illus- tration. A few of the anterior segments of an earthworm were cut off, H, Fig. 57, and from the remaining body a piece ah was cut from the anterior part of the nerve cord (see Fig. 57), while all the other tissues remained unaltered. The anterior cut end a of the worm healed, and no new head formed at this place. Instead, a new head was formed in some such cases at h, at the anterior cut end of the nervous system. If the head alone is cut off in an earthworm without the excision of the anterior piece of the nerve cord, a new head is formed at the anterior end of the body. In another series of experiments Morgan cut off the head H of an earthworm and in addition (Fig. 58) excised a piece he from the nerve cord, so that now two anterior cut ends, a and c, Fig. 58, of the nerve cord existed. In a few of these cases two new heads were After'morgan. AFfER
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