The developmental relationship between the nervous system and peripheral fields has been demonstrated repeatedly in a variety of animals. The investigations of Steinitz ('06), Braus ('06), Shorey ('09), and Durken ('11, '13) have shown that the removal of peripheral areas such as eye or limb influences the growing nervous system. The results of their experiments showed hypoplastic development of the analogous nerve center. Later investigators approached the problem by studying other peripheral areas. Workers have also shown that an overloaded periphery stimulates hyperplastic development of the specific nerve centers. Results from investigations on the influence which the eye has upon the development of the midbrain have been reported. Steinitz ('06) removed both eyes of Rana fusca larvae of 15 mm, and noted at metamorphosis that the optic lobes were smaller than in control animals. The opticus layer in which the optic nerve fibers normally terminate was thinner than normal. The midbrain also appeared flatter and narrower than normal.Durken ('11, '13) operated upon embryos of Rana fusca rather than upon larvae. He removed only one eyeball. The experimental animals were studied only in the metamorphic period. Durken reported a thinning and flattening of the roof of the midbrain which involved the superficial (opticus) layer. The deeper layers were affected also but to a lesser degree.Larsell ('29, '31) in his experiments on excision of one eye in larvae of Hyla regilla measured the thickness of the layers of the optic tectum in the affected and normal optic lobes. He noted a hypoplastic condition of the contralateral optic tectum. Larsell also noted that the neuroblasts of the 8th and 9th layers, which were most directly affected by the experiment were reduced in number. He concluded that his results appeared to be due to the absence of the normal functional stimuli which reach the optic lobes in the normally developing frog or to the absence of factors directly attributable to these stimuli.Goodman ('32) working with 9-day-old rabbits blinded the right eye of three mimals with light proof blinders, and enucleated the left eye in two animals, and then sewed the eye lid of one animal. The animals were kept in a dark room. The dark room animals with the left eyes excised soon after birth showed degenerative changes in the cerebral stump of the left optic nerves, right optic tracts, and the right primary optic centers. The unoperated dark room animals presented no differences from those of the controls in size in any part of the accessory optic apparatus, and there were no differences in the optic nerves. Goodman concluded that complete lack of optic stimuli in rabbits from birth to 6 months of age results in no observable changes in the visual pathways nor is there any evidence that the presence of the peripheral sensory visual field is a factor in the development and differentiation of the optic system in rabbits, or in the ability of that system to function. Kollros ('47, '48) removed one eye fromRana pipiens embr...
