320 STEREOTROPISM 



The Musculature. 



The muscles which determine the movement of the ray are classified 

 by position as (a) circular and longitudinal muscles of the dorsal 

 sheath, and {h) interskeletal longitudinal muscles of the ray floor. - 

 The action of the sheath muscles may be demonstrated in the intact 

 animal by stimulating the tip of the ray with a drop of 0.1 n acid. 

 As a result the ray shortens, due to contraction of the longitudinal 

 muscles, and suffers a decrease in diameter from the contraction of 

 the circular ones. Similar results are to be obtained with strong 

 stimulation of the tube feet of any part of the ray, thereby proving 

 the nervous connection of the sensory cells of the tube feet with the 

 muscles of the sheath. 



The most complex action of the neuromuscular system is seen in 

 the righting response. Here certain arms bend dorsally, others 

 ventrally, in response to reciprocal impulses.'' Obviously it greatly 

 aids an analysis of such reactions if the investigator can produce 

 them at will artificially or entirely apart from their normal causation. 

 This is made possible in the case of the starfish ray through the use of 

 the alkaloids, strychnine and nicotine.'* With strychnine the ray 

 bends dorsally, with nicotine ventrally. The parts played by the 

 various groups of muscles may be shown by separating the dorsal 

 sheath from the floor of the ray by cutting the two structures apart 

 longitudinally. When put into either nicotine or strychnine the 

 dorsal sheath shows dorsal flexure and rolls together so that the cut 

 edges meet and overlap. This demonstrates physiologically the 

 existence of longitudinal and circular muscles in the dorsal sheath. 

 In similar fashion the presence of dorsoflex and ventroflex musculature 

 in the floor of the ray may be shown, since in nicotine the floor bends 

 ventrally, in strychnine dorsally. 



There are therefore four muscle groups which play a part in the 

 movements of the ray. {a) The longitudinal dorsoflexors of the 

 sheath; {h) the circular muscles of the sheath, effective in twisting 



- Bronn, H. G., Klassen und Ordungen des Tier-Reichs wissenschaftlich 

 dargestellt in Wort und Bild, Leipsic, 1899, il, 3A, 543. 



' Loeb, J., Comparative physiology of the brain and comparative psychology, 

 New York, 1900, 61. Moore, A. R., Am. J. Physiol., 1910-11, xxvii, 207. 



* Moore, A. R., /. Gen. Physiol, 1919-20, ii, 201. 



