164 



E. LUCILE MOORE. 



Such variable results were obtained, however, that it is impossible 

 to say whether there is a tendency for Planaria to become less 

 sensitive to repeated doses or not. By looking over the per- 

 centages of decrease it may be seen that eleven of the twelve 

 animals responded to a lesser degree to the second treatment 

 than to the first; but there is one great exception, and there is, 

 in addition, the result, not recorded in the table, of a third test 

 made with the last series where the decrease was 47 per cent., 

 less than the first but greater than the second. Such variation 

 was to be expected, from the nature of the problem, since the 

 difference in the rate of locomotion does not express the whole 

 of the effect. Although these last experiments add nothing 

 new to our knowledge of planarian reaction to adrenin, they do 

 distinctly confirm the fact that adrenin produces a slowing of 

 the rate of locomotion through an over-excitability which expends 

 itself to no effect. 



TABLE II. 



The innervation of the muscles of Planaria has not yet been 

 worked out, but it is probable, from the simple character of the 

 nervous system, that the action of adrenin is directly upon the 

 muscle and not through the nerve endings. This point, however, 

 could not be successfully tested. In an attempt to ascertain 

 the role of the nervous system it seemed desirable to compare 

 the reactions of the anterior ends of the animals with those 

 of the brainless parts, when exposed to the same solutions of 

 adrenin. A number of individuals were cut in two just posterior 

 to the brain region, and the wounds allowed to close over. It 

 was practically impossible, however, to obtain any satisfactory 

 rates from these pieces even in water, as the small head ends 



