This is the founding work of modern biology written by Aristotle about 2300 years ago. It was one of the 1st systematic analyses of what we would now call The Five Kingdoms. However, the main benefit of the Parts Of Animals is not the factual information it provides... It is the use of a rigorous Scientific Method displayed in this work that makes it such a landmark. Scientists even today look back it as a guide. Unfortunately, it is no longer required reading at most univerities (though we do study it both freshman and sophomore year at my school, St. John's College). I stress again that this work is not valued for its facts... Aristotle was wrong on many accounts (a more humorous one is that the seal is a deformed quadraped). But if you get a chance, check this out of your library. I recommend the Oxford classical translation, though a much awaited translation by Joe Sachs is rumored to be coming out soon. And I think there is at least an excerpt in Hippocrates G. Apostle's Select Works... though I am not sure.