PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 107 



somewhat lower, but still finally lethal concentrations, the impulses from 

 the apical nervous organ decrease in frequency so long before the more 

 oral regions of the row are appreciably injured by the agent that these 

 latter regions become physiologically isolated (pp. 327-28) and develop 

 a vigorous beat entirely independent of the apical region, while the aboral 

 part of the row is much less active or its plates have ceased to beat. If 

 these conditions persist for an hour or more before death, the more active 

 plates toward the oral end of the row may die before the less active or in- 

 active aboral plates. The change of the plates to opaque white at death is 

 apparently due to coagulation of their colloids. When movement is in- 

 hibited soon after exposure to the agent and death occurs in an hour or 

 two, the base of each plate becomes white earlier than the plate itself, and 

 the change in appearance progresses from base to tip of the cilia compos- 

 ing the plate. When active movement of plates continues for several 

 hours during exposure to the agent, with final death, coagulation begins 

 at the tips of the cilia and progresses basipetally in each plate, the plate 

 base being the last to undergo the change. 



The lobate genus BoUnopsis is extremely sensitive and often undergoes 

 complete and practically instantaneous disintegration when subjected to 

 sudden shock. Disintegration may be induced by sudden exposure to cer- 

 tain chemical agents, but with different concentrations or rates of addition 

 of the agent to sea water the degree of disintegration may be varied and 

 controlled. In concentrations near the lower limit of shock effect disin- 

 tegration may occur only after several seconds or even i or 2 minutes. In 

 such cases disintegration begins at the apical (aboral) pole and at about 

 the same time at the tips of the oral lobes and progresses orally over the 

 body and aborally in the lobes. It may progress from the apical pole over 

 a fourth or a third of the body and stop, leaving the rest of the body, or all 

 except the tips of the lobes, intact. In short, the disintegration gradient 

 following shock is the same as the death gradient in slowly lethal agents 

 which do not produce shock effect (Child, 1917c, 1933a). The ctenophore 

 plate row is a particularly good example of a gradient with functional ex- 

 pression showing relations of dominance, subordination, and physiological 

 isolation and under some conditions even reversal in direction, essen- 

 tially similar to relations and alterations in developmental gradients. The 

 reversal in direction of the death gradient in the cilia of the plate in rela- 

 tion to quiescence and motor activity is another feature of interest. The 

 changes in the ctenophore plate row do not result in altered morphological 

 development, but they do bring about altered functional development. 



