Control of Luminescence in Hemichordates and Some Properties of a Nerve Net System.

Since 1875, when Panceri first described luminescence in a hemichordate, Glossobalanus minutus, four other species of enteropneusts have been observed to emit light Delage & Herouard (1898) reported that luminescence of Balanoglossus clavigerus from the coast of Brittany was bright enough to be seen even in the presence of candlelight Kuwano (1902) described luminescence in Balanoglossus misakiensis from Japan; Crozier (1920) and Harvey (1926) found the response in Ptychodera bahamensis from Bermuda, and Rao (1954) in Ptychodera flava from India. Judging from the species examined which do not show luminescence, Harvey suggested (1952) that this response is confined to the family Ptychoderidae, to which these genera belong. Crozier (1920) reported that Ptychodera shows a diurnal rhythm in the production of luminescence and could be made to emit light during the day only if subjected to electrical or to very strong mechanical stimuli. Harvey (1926) was unable to observe this rhythmicity, and found that species from both Bermuda and the Mediterranean would luminesce during the day without unduly strong stimulation. Crozier, Harvey and Rao have agreed that luminescence is inhibited by light and that it was necessary to keep animals in darkness a few hours in order to evoke a response by mechanical stimulation. The production of light occurs all over the body except in the gill region (Crozier, 1917; Rao, 1954); it has been thought to be caused by the emission of a luminous slime. Virtually nothing has been reported on the control of luminescence in the group. Panceri comments that he could observe no luminescent waves in these animals, as were sometimes present on the surface of pennatulid coelenterates. Dahlgren (1917) described goblet cells in the epidermis of Ptychodera bahamensis which he concluded must be the photogenic cells, and Bullock (1940) has described the intra-epidermal nervous system, but anatomical connexions have not yet been found between the two. The present study was undertaken to investigate the nature of the luminescent response in greater detail, particularly with regard to the role played by the nervous system in eliciting the response. This is of special interest since little is known of the physiological organization of the enteropneust nervous system. Knowledge of the characteristics of the nerve net of enteropneusts would allow a comparison with the well-studied coelenterate nets to determine common denominators of neural activity existing at similar levels of organization in phylogenetically diverse groups.