DISUSE AND DEGENERATION.* 
One of the several much-discussed but little-tested problems of the 
theory of evolution is that of the inherited effects of disuse. I believe that 
thereis a pretty general idea that when a species no longer has need for 
an organ that organ will degenerate. The explanations of this degener- 
ation are varied, but the most popular seem to be the inheritance of 
acquired characters, panmixia and selection. It is indisputable that in 
the life of an individual many unused organs do degenerate, but it is far 
from proven or even satisfactorily indicated that this ontogenetic degen- 
eration is followed by a phylogenetic degeneration. There is no doubt 
that many degenerate organs are not used in any way; but who can say 
whether this disuse has preceded degeneration as a cause or merely fol- 
lowed as a necessary consequence ? Before attempting to explain the 
phylogenetic degeneration which follows disuse it seems desirable to find 
a clear case of such a sequence, and this quest was the purpose of the 
experiment with Drosophila ampelophila upon which I wish briefly to 
report. 
These insects are normally very good fliers, possessing wings which 
are relatively quite large. Inmy exveriments, however, they were con- 
fined in glass vials barely large enough to contain the food. The only 
opportunity they had to fly was when they were transferred from one 
vial to another. This was done only three times a week. Such flight 
could at most not be more than 5cm., and was, as a matter of fact, 
rarely made, as they usually walked. 
The experiments are complicated by several facts which must be con- 
sidered. These fall into two groups: 
First, those which might explain the absence of degeneration in the 
wings. Disuse does not affect, during the life of an individual, the 
wing-dimensions, for after an insect’s wings are expanded there is no 
change in them and, of course, they are not subject to the effects of use 
and disuse before they are expanded. However, the degeneration of 
beetle-wings when the elytra are fused, of the wings of cave insects, of 
parasites, and of the wings of many female Lepidoptera are used as stock 
examples of disuse. Furthermore, if there be anything in the theory 
of hormones (of which Cunningham has recently made so much) or the 
various forms of the memory theory of inheritance, we would expect 
phylogenetic degeneration because of the germ-plasm receiving the news 
that the wings are not being used, providing the plasm is in condition to 
*Paper read before the American Society of Zoologists, Baltimore meeting, 1908. 
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