BEHAVIOR OF HOLOTHURIANS IN BALANCED ILLUMINATION 513 



surimimensis or H. captiva exhibit local wrinkling contractions when a 

 spot of intense light is thrown upon them. The wrinkling movements 

 cease when the strong light is removed. When first prepared, the 

 pieces of the body wall are strongly contracted; but if they be allowed 

 to lie in seawater for half an hour or so, or if they be subjected to gentle 

 traction, they become somewhat relaxed, although the cut edges remain 

 curled. It was on such relaxed preparations that the light test was 

 made. Tube feet on isolated portions of the "ventral" surface also 

 bend away from the light. 



b. A phenomenon closely akin to "circus movements," and probably 

 in principle identical with them, appears when these holothurians are 

 exposed to general illumination from above, provided one side of the 

 animal's surface has been rendered insensitive to light. In the narco- 

 tizing, cocaine seems to give the best results, but chloretone was also 

 used. In the case of either narcotic, a strong solution (in seawater) 

 was employed and the holothurian, while being held out of water, had 

 one side painted over with the solution several times. The parts so 

 treated soon become quite insensitiv'e to light, while the untreated side 

 is still sensitive, and its tube feet all remain normally functional. On 

 being returned to seawater the holothurians soon assume a curved atti- 

 tude, the narcotised side being the relaxed one (convex). If the ani- 

 mals are then strongly illuminated from above, they rapidly become 

 curved in the opposite direction, the narcotised side being then the 

 inner, contracted '(concave) portion of the bend. Thus the holothur- 

 ian bends toward the unstimulated side, whether the non-stimulation is 

 determined by the relative absence of light, or by the enforced inca- 

 pacity of its photoreceptors. 



VI. These experiments afford evidence: (1) that the amount of light 

 received by the photosensitive surface of Holothuria surinamensis and 

 H. captiva determines their behavior in an illuminated field; (2) that 

 the assumption of a definite path of progression, with respect to bal- 

 anced illumination, depends on the non-parallel relation of photosensi- 

 tive surfaces. 



BIBLIOGRAPHY 



(1) LOEB: Studies in general physiology, Chicago, 1905, Part I, 13. 



(2) PATTEN: Journ. Exper. Zool., 1914, xvii, 213. 



(3) PATTEN: This Journal, 1915, xxxviii, 313. 



(4) CROZIER: This Journal, 1914, xxxvi, 8. 



(5) CROZIER: Zool. Jahrb., Abt. Physiol., 1915, xxxv, 233. 



(6) CROZIER: Sci., N. S., 1916, xliii, 148. 



THE AMERICAN JOURNAL OF PHT8IOLOGT, VOL. 43, NO. 4 



