Sentence:  Laurence M . Klauber put length at maturity at two thirds the ultimate length for some rattlesnakes , and Charles C . Carpenter 's data on Michigan garter and ribbon snakes ( Thamnophis ) show that the smallest gravid <WSD>females</WSD> are more than half as long as the biggest adults . 
Meaning of the word marked with <WSD> tags:  an animal that produces gametes (ova) that can be fertilized by male gametes (spermatozoa)