Implications of the Theories of Nerve Action 191 



arthropods, and especially in the one on the segmental the- 

 ory in vertebrates. 



The starting-point chosen by Loeb for the treatment is 

 the earthworm. It is generally known that this animal is 

 jointed, or segmented, that every segment has a pair of nerve 

 ganglia situated underneath the intestine on the floor of 

 the body wall, and that the pairs of ganglia are all connected 

 with one another fore-and-aft, so that the whole constitutes 

 a chain of ganglia extending the entire length of the body. 

 In addition to this series of ventral ganglia, there is a pair 

 of large ganglia above the gullet at the extreme front end 

 of the creature, these being connected with the ventral nerve 

 chain by commissures. These dorsal nerve masses are usu- 

 ally called the supra-esophageal ganglia, but are often 

 spoken of as the brain. 



On the basis of the "center" theory of the nervous sys- 

 tem, it was very natural to raise the query: Is the earth- 

 worm's brain the "seat", the primal source of the coordi- 

 nated activities, the crawling and burrowing which make 

 up so large a part of the life activities of these crea- 

 tures? Loeb's own formulation of the question is good. 

 "Does coordinated progressive movement in which all the 

 segments of the body participate, depend upon the brain?" 



The first attempt to answer this question experimentally 

 seems to have been made by Friedlander. Having made a 

 small opening in the side of the body of a living worm and 

 cut out a piece of the nerve cord so that a complete hiatus 

 in the cord was produced, the author fully expected, he tells 

 us, that after the healing of the wound in the body wall, 

 which took place very quickly and completely, the parts of 

 the body in front of and behind the section of the cord would 

 either behave like two separated individuals, or that the 

 front part would draw the rear part passively about. But 

 neither result followed. "Animals from the middle of which 

 a piece of the central nervous system is wholly wanting, 



