Nerves in the endodermal canals of hydromedusae and their role in swimming inhibition.

N eoturris breviconis (Anthomedusae) has a nerve plexus in the walls of its endodermal canals. The plexus is distinct from the ectodermal nerve plexuses supplying the radial and circular muscles in the ectoderm and no connections have been observed between them. Stimulation of the endodermal plexus evokes electrical events recorded extracellularly as "E" potentials. These propagate through all areas where the plexus has been shown by immunohistology to exist and nowhere else. When Neoturris is ingesting food, trains of "E" potentials propagate down the radial canals to the margin and cause inhibition of swimming. This response is distinct from the inhibition of swimming associated with contractions of the radial muscles but both may play a part in feeding and involve chemoreceptors. Preliminary observations suggest that the "E" system occurs in other medusae including Aglantha digitale (Trachymedusae) where the conduction pathway was previously thought to be an excitable epithelium.

Scanning electron microscopic observations of the development of the somites and their innervation in anuran larvae.

The development of the paraxial mesoderm in tadpoles of Xenopus, Bufo and Rana was observed with a scanning electron microscope. In addition to examination of the differentiation of the surface and the interior of the somites, some attention was also paid to the transformation of the material of the neural crests and to the innervation of the developing myotome.