Developmental-physiological relations between the limbs of Amphibia and their innervation
Naturwissenschaften 15(32): 657-661
To study the influence of nerves on the developing limb of the frog embryo, the part of the spinal cord supplying the hind limbs was excised. Bilateral and unilateral operations were done just before closure of the neural folds on embryos of Rana fusca and Bombinator pachypus. The unilateral type was preferred as mortality was less, and the normal side served as a control. In [image] of the animals reaching metamorphosis the excised piece of spinal cord regenerated and the animals were entirely normal. In the remainder growth but not differentiation was arrested, so that at metamorphosis the limb was considerably shorter than its control; it was stiff-jointed and the muscles were atrophied. Sections showed, in some cases, small nerves in the operated limbs, while in more strongly affected limbs there were only a few twigs or no nerves at all. In one case the limb was supplied with small nerves from the 12th spinal ganglion, which normally disappears at metamorphosis; in another, the operated limb had attracted nerves from the lumbar plexus of the unoperated side. All limbs were paralyzed, thus showing that nerve supply and function are not necessary for normal development. Disturbances resulting from absence of nervous influence, such as shortening, stiffness of joints, and atrophy are not of a morphogenetic nature, and can be explained as being due to defective nutrition of the limb and to absence of muscle tonus and function. The author admits that it is difficult though not impossible to reconcile this work with that of Durken, which he had previously confirmed, and he proceeds to explain his former results. There is an excellent account of the literature dealing with relations of the developing limb to the nervous system.