CONDUCTION IN THE NERVE-FREE EPITHELIA OF SIPHONOPHORES

Optical and election microscopy leave little doubt that nerve and muscle fibers are completey absent from large stretches of the epithelium covering the swimming bells in siphonophores (Class Hydrozoa). Behavioral experiments show that these regions must conduct, and electrophysiological evidence of propagated depolarizations in the epithelial cells has been obtained. Conduction velocities are in the order of 20-50 cm/sec, and a refractory period of 2-3 msec has been measured. Conduction is non-decremental and unpolarized.Non-nervous conduction probably occurs in other siphonophore tissues (two examples are discussed), and it may be important in the behavior of many Hydrozoa.