On the Nervous System of Cassiopea Xamachana. 147 



influence is necessary for the formation of normal structures in regenera- 

 tion, as Herbst (1896 and 1899) concluded from his experiments on 

 decapods; or as maintained by several of the earlier workers upon 

 regeneration in platodes, and by Walter (1911) for Triton. The second 

 of these special cases has been shown by the studies of Morgan, Child, 

 and Goldfarb to be conditioned by influences other than the presence of 

 the nerve-centers. The work of Steele has shown also that in several 

 species of Crustacea the removal of an eye-stalk is not followed by the 

 regeneration of a heteromorphic structure. 



While none of these workers has laid any stress on the fact that the 

 nervous system exerts an influence on the rapidity of the early stages 

 of regeneration, it has been noted in several instances that the initial 

 stages of regeneration are more rapid in the control animals than in 

 those from which the nervous system has been removed. Thus, 

 Goldfarb {op. cit., page 664) states that in salamanders the hind limb 

 develops more slowly on the side from which the dorsal ganglia inner- 

 vating the leg had been removed than does that of the opposite side 

 in which the ganglia remained when the spinal cord had already been 

 removed. In a table on pages 665 and 666 he shows that this result 

 was observed in all the specimens recorded save two, in one of which 

 the regeneration was, at the time of measurement, equal for both legs, 

 while in a single specimen the regeneration was most rapid from the 

 side from which the ganglia were removed. 



In tadpoles from which the caudal portion of the spinal cord had 

 been removed regeneration of the tail took place more slowly than in 

 the control animals in which the cord was uninjured (p. 672). Again, 

 concerning earthworms from which the head had been cut off and 

 several millimeters of the ventral cord removed he says (p. 708): 

 ''The head regenerates rather later in these operated animals than in 

 control animals." In the regeneration of the arms of the starfish 

 (p. 711) a similar observation is recorded. 



Goldfarb, however, is of the opinion that "any severe injury * * *, 

 whether involving the nerves or any other tissue, retards regeneration." 

 Stockard, on the other hand, concluded that in Cassiopea, as Morgan 

 had already shown for a considerable number of animals, the rate of 

 regeneration increased in proportion to the extent of injury and that 

 the deeper the cut — i.e., the nearer to the center of the disk— the faster 

 would be the following regeneration. 



In my experiments the amount of tissue removed from the margin 

 of each half of any disk was the same. The differences in result 

 observed were, therefore, due to the difference in kind, not in quantity 

 of tissue removed. As recorded previously, the difference in rate of 

 regeneration is in Cassiopea greatest in the early stages and gradually 

 declines thi'oughout its course, at least through the periods followed in 

 these expermients. Goldfarb's observations appear also to show a 



