Trilobites are perhaps the most successful group of animals ever to live. Named for their distinctive three-lobed body, these armored, pill-bug-like arthropods were some of the first hard-bodied ...

Sexual reproduction is the production of a new organism from two parents by making use of their sex cells or gametes. The humans, fish, frogs, cats and dogs, all reproduce by the method of sexual ...

What purpose does the penis serve? Why is it that members of one species have no penis at all, while those of another have two? Why do they vary so much in shape and size? And where do vaginas, or the ...