ABSTRACT
A brief description is given of some features in the special morphological organization of the neuromuscular system in the embryo of the lower vertebrates.
The development of locomotory behaviour patterns in elasmobranchs is compared with that in other groups.
The earliest movements of the embryo of Scyliorhimis caniculus have been photographically recorded ; the results of Wintrebert are confirmed. The movements persist unchanged after complete removal of the nervous system ; they are rhythmical and independent on the two sides. Any isolated portion of an actively contracting myotome band can act as its own pace-maker.
The histological structure of the nerve cord and muscle at the time of these first movements is described in detail. There is strong evidence against any morphological link between the motor neurons and the myotome band; other neurons in the developing spinal reflex arc are similarly unconnected with one another.
The results are discussed in relation to similar phenomena in other systems. Consideration is given to the mechanism of the excitation and transmission of the contractile process in the myotome band.
