164 Charles W. Hargitt 
observers, among them Patten, whose comment was cited in the 
previous paper (p. 312). 
In an interesting article on the behavior of these annelids Ada 
W. Yerkes® has expressed doubt as to the question of fatigue, but 
seems to have misinterpreted the significance of the term as em- 
ployed in my paper, and has, [ think, misapprehended my con- 
clusions. For example, I did not attribute the failure to react 
under rhythmic stimuli to fatigue, as Mrs. Yerkes has suggested. 
What I did say was, “In connection with this matter of rhythmic 
shadows it was observed that where experiments were repeated 
with any considerable frequency specimens sooner or later be- 
came somewhat irresponsive, often failing entirely to react to any 
of the usual tests. Yhzs I am inclined to regard as the result of 
fatigue’ (p. 301). Concerning the failure of response under 
rhychmic stimuli my words were: “ May it not be possible that in 
these rhythmic shadows we have a simulation of the more or less 
rhythmic shadows resulting from the ripples of wave action.” As 
will be seen, therefore, my suggestion of fatigue had no reference 
to the matter of rhythm, but to the long-continued experimenta- 
tion which was designed to induce reactions repeated up to the 
point of fatigue. Furthermore, it was explicitly stated that under 
the normal conditions of rhythmic wave action such shadows 
might be assumed to have ceased to act as definite stimuli, the 
creatures having become accustomed to their effects by reason of 
their constancy. It seems to the writer that the above account 
of later experiments, with others of similar nature, goes far to 
confirm the earlier view. As one carefully observes such behav- 
ior it is difficult to escape the conviction that something akin to 
fatigue of some sort is involved. It may be that certain sensory 
cells only are affected, or it may be that certain central ganglia 
are involved, whose cells have to do with sensory and muscular 
coordination. 
Some recent work on the problem of fatigue in nerve cells by 
Drs. Smallwood and Rogers® has thrown new light on the subject 
and furnishes convincing evidence as to:changes in the cells them- 
5 Jour. Comp. Neurol. and Psychol., vol. xvi, p. 442. 
® Jour. Comp. Neurol. and Psychol., vol. xviii, p. 67, 1908. 
