of Medicine, Califo?-nia
The literature on the nature of the early spoiitaneous somatic movements in teleost embryos is characterized by marked disagreement, two extremes being represented by Tracy ( '26) who considered them to be neurogenic, and Coghill ( '33) who concluded that they were myogenic. Wintrebert ( '20) prior to Tracy's work, had demonstrated conclusively that early movements in selachians were of a myogenic nature: they continued after complete removal of the spinal cord. But Tracy ('26, p. 264) maintained that in teleosts, including Fundulus, the " 'myogenic' stage never appears. " He believed that the spontaneous movements were, from their first appearance, under the control of motor nerve cells and that these motor neurons were stimulated by CO, in the internal environment. The frequency of the movements was increased by raising the CO, tension of the external environment. The neurogenic hypothesis was supported by the fact that motor nerve pathways could be demonstrated as early as the time of first somatic movements. Coghill ('33) observed that the spontaneous movements were not affected by curare, a drug known to paralyze the adult myoneural junction, and this observation led him to consider the movements as my ogenic.
The evidence supporting the claims of both Tracy and Coghill was criticized in Barron's ('41) review. Barron disagreed with Tracy's contention that CO, stimulates nerve cells and he cited evidence of C0,-asphyxiation of motor centers. On the other hand Barron criticized the use of curare to establish a claim of myogenic activity in the embryo, because the actions of the drug on the embryonic and adult neuromuscular junctions have never been shown to be identical.
In view of the fundamental disagreement between the conclusions of Tracy and Coghill and Barron's criticism of their supporting evidence, it appeared desirable to reinvestigate the problem with a new a Now in the Department of Anatomy, Duke