Summary and Discussion 219 
Concerning Roubaud’s observations on the larvae of the African 
fly which come out of the earthen floor at night to feed upon 
the natives sleeping on the bare ground, he concludes: ‘‘This 
periodicity is the result of thermic sensibility. This rhythm not 
only is acquired in the course of the larval existence, but is 
changeable at the will of the experimenter.’’ These and other 
conclusions drawn for the most part from inadequate observa- 
tions, are obviously self-contradictory. 
But this condition of chaos in the literature regarding 
rhythmic periodicity serves to bring to light a significant point 
in this new field of study. It is evident that this comparatively 
new term, rhythmic periodicity, has caught the ear of many in- 
vestigators, and intrigued them to either attempt to explain the 
phenomenon without defining it, or more often, to apply the 
fascinating term, as though it were a final explanation, to any 
regularly recurring action discovered in their material. Thus 
in the above instance, the action of the African fly larvae in 
coming out at night to feed upon the natives when they lie 
down on the ground is ponderously explained ; ‘‘This periodicity 
is the result of thermic sensibility,’’ although a few lines fur- 
ther on the author naively explains that the creature’s ‘‘rhythm 
is changeable at the will of the experimenter.’’ To call this 
action ‘‘rhythmie periodicity,’’ when the creature merely turns 
to its food supply when the latter intermittently comes near, 
is obviously far-fetched. Many phenomena explained by various 
authors as ‘‘rhythmic periodicity’’ are merely adaptations or 
even temporary adjustments to a regularly recurring feature 
of the environment. The clover spreads its leaves to the sun 
during the day to make its growth; the rabbit slips out to 
nibble the clover at night so he may escape the hawk; the owl 
sleeps during the day so he may come out and get the rabbit. 
All of these actions, taken separately, have been attributed to 
rhythmic periodicity, yet not one of them would continue its 
action rhythmically (by the clock) at all if the object of its 
quest changed habit. Of course these adjustments to environ- 
ment or fellow-creatures entail morphological modifications in 
the organism—the eyes of the owl, the eyes of the hawk, ete., 
but whether the habits have caused structural variations, or 
whether morphological changes have induced new habits is a 
problem that is outside the scope of this paper. Pursuing a 
