Word Study
proleg
CIDE DICTIONARY
proleg, n. [Pref. pro- for, in place of + leg.].
One of the fleshy legs found on the abdominal segments of the larvæ of Lepidoptera, sawflies, and some other insects. Those of Lepidoptera have a circle of hooks. Called also proped , propleg , and falseleg . [1913 Webster]
OXFORD DICTIONARY
proleg, n. a fleshy abdominal limb of a caterpillar or other larva.
Etymology
PRO-(1) + LEG
For further exploring for "proleg" in Webster Dictionary Online