The foregoing comparison of the anatomy of the apterous viviparous and the winged viviparous stages of S. rosarum although not revealing any very great differences, may be regarded as supporting the view that the apterous stage is a degeneration from the winged stage. The fact that so much similarity exists between the two forms is perhaps more easily explained by supposing that the habit of flight had become eliminated, possibly through disuse, resulting in the consequent atrophy and disappearance of the organs directly concerned with that function; for if the other view be considered, it would be reasonable to suppose that more specially marked differences in an upward direction would be the result of such a vital change in the habit of the creature. There is one point of difficulty, however, and that is to account for the difference in form of the alimentary canal, but, as has been already suggested, this may be due to other, quite different, and at present unknown, causes.