text: is there some sort of animal where the babies hatch out of holes in the mother's back?  maybe a fish or frog? i have this weird memory that i've watched a nature special about it, but i've searched and googled and can't find anything like it. frogs and toads display some of the most amazingly varied breeding behaviors and mechanisms :-) the surinam toad (pipa pipa) is an aquatic species in which the eggs, after being fertilized during a complex courtship,  are placed with the aid of the male on the back of the female, embedded in the skin. the eggs do not undergo indirect developmet as in most frogs (they don't hatch as tadpoles), instead, after 3/5 months they emerge as young juvenile frogs.  more information from animal diversity web: http://animaldiversity.ummz.umich.edu/site/accounts/information/pipa_pipa.html  in addition, there are some frogs in south america known as "marsupial frogs". these are tree frogs in which the female has a dorsal pouch of skin on her back, and the eggs develop inside this pouch. after hatching, they come out of the pouch opening that opens posterodorsally.  this is what the female with the eggs looks like: http://nature.berkeley.edu/~screws/trinidad%20dir/images/img_1411.jpg  and there's another amazing frog here in argentina: the tiny green darwin frog that lives in the southwestern forests. in this species, the male takes the eggs after they've been fertilized and puts them in his vocal sacs (the pouches at his throat that he uses to produce sounds). they stay in the vocal sacs until they're more developed and can come out and go on growing by themselves. http://www.globalamphibians.org/images/rhinoderma_copyrighted.jpg i know this has nothing to do with the question, but i think these are so interesting! :-)