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1 1 | consider the parts which are useful to animals for movement
2 10|     for swiftness of wing is useful to their mode of life.)
3 11|      the wings are naturally useful to it, but if it were erect
4 15|   The reason is that this is useful for ease in creeping into
5 17|      the crayfish; a tail is useful to the crayfish for swimming,
6 17|    feet. Broad feet are more useful than long for pushing away
7 18|     water, not air. Fins are useful for swimming, but feet not.