4 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



■worms from which the first (about ten) segments of the body have been 

 removed. 



6. Stereotropism (Tactile response). — Examine the stereotropic 

 response when the animal is creeping in lateral contact with a glass plate. 

 Turn the earthworm on its dorsal surface. Describe result. How could 

 you show that the righting response is due to stereotropism? Try it and 

 describe the result. The inverted worm may be suspended by two threads. 

 Focke (Zeit. wiss. Zool., 136: 376, 1930) claims the righting reaction is 

 not a gravity effect. 



6. Chemical Sensitivity. — Test response of the earthworm to local 

 application of a drop of M/10 KCl. What region of the body is 



PORSflL RAMUS OF flNTEHIOR 

 SESMENTflL NERVE 



CEREBRAL GANGLION 



PROSTOMlun 



Fig. 1. — Relative positions of the brain and ventral nerve cord in the earthworm (after a 

 drawing by Prof. W. N. Hess in Roger's Textbook of Comparative Physiology, McGraw-Hill). 

 Focke (Zeit. wiss. Zool., 136 : 385, 1930) describes how the brain may be removed by a hooked 

 wire inserted by way of the mouth. 



most sensitive? Arrange several regions of the body in order of their 

 sensitivity. 



7. Galvanotropism (Orientation by electric current). — Place a worm 

 on a moist glass plate and pass current from one dry cell transversely 

 through the middle segments by means of non-polarizable electrodes made 

 of glass tubing containing Ringer's fluid and plugged with cotton. Do 

 the ends turn toward the cathode? Carefully sever the nerve cord on 

 each side of the stimulated region and repeat the experiment (cf . Moore, 

 J. Gen. Physiol., 5: 453, 1923). 



8. Influence of the Brain on Sensitivity. — Narcotize a worm slightly 

 with chloretone. Carefully cut through the dorsal body wall of the 

 third somite. (Fig. 1.) With a hot needle destroy the cerebral hemi- 



