The Locomotor Behavior of Spinal Elasmobranchs with an Analysis of Stinging in Urobatis

Abstract

the members of the phylum Chordata as the possession of a flexible notochord. This swimming behavior is exhibited, in a simple or as a derived pattern, by all forms with the exception of the sessile adult ascidians. The interdependence of these two basic features has been suggested and ably supported by de Lange (1936), whose discussion of the morphology of the chordates emphasizes the relation of the body column and its associated metameric musculature to swimming. According to this interpretation, the segmented effector (muscle) system arranged along the semi-rigid notochord serves the primitive or Urtyp locomotion. The phylogeny of the locomotor behavior should be related to the evolutionary history of the skeletal framework, its associated musculature and to the neural integrative apparatus to achieve the full picture of evolution within the phylum. The nervous structures which integrate this behavior are nowhere more revealingly discussed than in Coghill's (1929) treatise. This author has shown that the appearance of sinuous swimming and of longitudinally conducting motor-cell columns in the spinal cord, in the early Anmbystoma larva, go hand in hand. This has been amply substantiated by other authors. In the work of Coghill and his collaborators we find a careful tracing of this simple behavior system as it is modified by the developing sensory systems, the growth of limbs, of jaws and gills, and progressive encephalization. Teleosts, amphibians, birds and mammals are all considered. The various papers of this school are discussed and listed in Herrick (1949). In a previous paper (Campbell, 1940), I have discussed the undulatory swimming behavior of hagfish with intact and transected spinal cords. It was shown that the integrative mechanisms involved were spinal, not cerebral, though the brain influenced quantitatively the locomotor response and integrated it with the environment (righting reflexes, for example). Conditions governing the forward and backward motion of the undulatory waves were explored and the effects of partial section of the spinal cord described. It was shown that immediately upon separation, an isolated portion of the spinal cord acts as-a whole, establishing a head and tail end with rather different properties and that the wave length of the undulations adjusts immediately downward as the spinal cord is rendered shorter. The pelagic sharks, as Gray and Sand (1936) have pointed out, utilize a purely undulatory type of swimming. The resemblance between the progression of these animals and that of the hagfish is striking. Yet certain complications have occurred in the swimming sharks. The development of jaws and of other specialized structures has enlarged the head to a considerable proportion of the entire body length and thus has removed much of the 1 Contributions from the Scripps Institution of Oceanography, New Series, No. 554. The valuable