TRANSMISSION OF MODIFICATIONS 395 



infolding and pressing the piece against the body as if endeavor- 

 ing to tuck it into a mouth, though none is present. 1 Here it is 

 not intelligence that affords the basis of muscular contraction 

 but chemical action of the meat juices upon the muscle fibers of 

 the tentacles. -The same principle governs motion and secretion 

 in insectivorous plants, to which no one would ascribe even the 

 elements of intelligence. Odors excite the salivary glands and 

 make the mouth water, but it is contact that starts the secre- 

 tion of gastric juice in the stomach. 



Light stimulates specific reactions in many forms of proto- 

 plasm, and many tissues contract under its influence. It is this 

 contraction that causes the bending of stems toward the light. 

 The iris of the eye contracts, not by nervous impulse but by 

 the action of the light, causing, directly, muscular contraction. 

 Loeb reports 2 that he has often observed the contraction of the 

 iris of dead sharks under the influence of light " several hours 

 after death, when signs of decomposition had already begun 

 to appear." 



Long-bodied insects, if lying with the side to the light, will, 

 because of this, have their bodies bent, with the concave side 

 next to the source of light if positively heliotropic. Whenever 

 they move in this condition they must of necessity move in a 

 curved instead of a straight line, until such time as they are 

 headed directly toward the light. From that time the body is 

 equally illuminated on both sides. It therefore becomes and 

 remains straight, so that future motion must be in a straight 

 line, any deviation being quickly corrected by the unequal illumi- 

 nation of the body. It is this series of facts, arising from the 

 natural relation between light and protoplasm, and not curiosity, 

 that accounts for the flying of the moth into the candle. Nega- 

 tively heliotropic animals would of course behave in exactly the 

 opposite manner, but for the same general reasons. 



Insects and small worms are said to burrow into dark places 

 for the purpose of hiding. This cannot be true, for under direct 

 experiment small animals often emerge from darkness to light, 

 from hiding to exposure, under the impelling force of an in- 

 stinct to bring their bodies into contact with as many surfaces as 



1 Loeb, Physiology of the Brain, pp. 48-54. 2 Ibid. p. 40. 



