THE FUNCTIONAL ORGANIZATION OF THE NERVOUS SYSTEM OF ENTEROPNEUSTA THEODORE HOLMES BULLOCK (From the Department of Zoology, University of California, Berkeley, California) INTRODUCTION The chordate affinities of balanoglossids have been widely accepted ever since Bateson advanced the suggestion in 1885 and have not seriously been challenged since Spengel (see especially 1893). Some of the most characteristic features of chordates relate to the nervous system. Moreover, the evolution of that group has outstandingly involved this system. It is of considerable interest, therefore, to inquire into the nature of the nervous mechanism of the Enteropneusta. Investigations of a purely morphological type were made by the earliest workers, but we lack, as yet, any conception of the functional stage of development represented or the plan of organization. The purpose of the present paper is to report some simple experimental evidence concerning the physiologic pattern of the nervous system in the Enteropneusta, and to offer a tentative generalized picture of its condition. The intimate relation between receptors, nervous mechanism, and effectors renders it appropriate, in the case of animals whose general behavior is unfamiliar, to consider all three systems as an integrated unit. Since our only knowledge of the activities of the first two named systems is gained through observations of the overt activities of the effectors, the latter system is treated first. The original observations contained herein relate chiefly to two eastern Pacific species, Saccoglossus pusillus (Ritter) (formerly Dolichoglossus) and Balanoglossus occidentalis (as yet a manuscript species). These were collected near San Diego, California, and the majority of the experiments were carried out in the laboratories of the Scripps Institution of Oceanography. It is a pleasure to acknowledge the kindnesses extended to me by Dr. H. U. Sverdrup and Dr. M. C. Sargent of that Institution. EFFECTORS AND THE CHARACTER OF RESPONSE The behavior of enteropneusts originates in at least three effector systems: ciliary, glandular, and muscular. 91
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