The dorsal epidermal nerve-tract is continued in front into the ventral wall of the collar nerve-tube, and at the point of junction there is a circular commissural thickening following the posterior rim of the collar and affording a special connexion between the dorsal and ventral nervetracts.
No organs of circulation or respiration are known; but the nervous system is well developed, and consists of a pair of ganglia corresponding with the limbs and connected by longitudinal commissural chords.
We have examined the morphology and longitudinal axon projections of a population of spinal commissural interneurons, in young Xenopus tadpoles.