The influence of the peripheral fields upon the development of both motor and sensory centers in the spinal cord was observed by Shorey ( ,09). Later workers have demonstrated that hyper-or hypoplastic development in the motor and sensory centers may be obtained by respectively increasing or decreasing the mass of the periphery to be innervated (for a review of the literature see Piatt, '48).
May ('30) produced sensory and motor hypoplasia by interposing spinal cord pieces between the developing limb and the host cord of Discoglossus pictus, preventing, in some cases, innervation of the limb by the host cord. Conversely, he was able to demonstrate hyperplastic development in the presence of supernumerary limbs (May, '32, '33a, '33b, '34).
His ablation experiments revealed a failure of the lumbosacral plexus to form, reduction in spinal cord size on the affected side, sensory hypoplasia, and lack of the motor horn at this level. Even in cases of partial regeneration of the limb complete absence of the motor horn was reported.
'This research was carried out under the sponsorship of Dr. J e r r y J. Kollros in partial fulfillment of the requirements f o r the degree of Doctor of Philosophy.