<P> Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg - laying (Latin . oviparous) from live - bearing (Latin . viviparous). </P> <P> These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body . Traditionally: </P> <Ul> <Li> Ovuliparity means the female spawns unfertilized eggs (ova), which must then be externally fertilised . Ovuliparity is typical of bony fish, anurans, echinoderms, bivalves and cnidarians . Most aquatic organisms are ovuliparous . The term is derived from the diminiutive meaning "little egg". </Li> <Li> Oviparity is where fertilisation occurs internally and so the eggs laid by the female are zygotes (or newly developing embryos), often with important outer tissues added (for example, in a chicken egg, no part outside of the yolk originates with the zygote). Oviparity is typical of birds, reptiles, some cartilaginous fish and most arthropods . Terrestrial organisms are typically oviparous, with egg - casings that resist evaporation of moisture . </Li> <Li> Ovo - viviparity is where the zygote is retained in the adult's body but there are no trophic (feeding) interactions . That is, the embryo still obtains all of its nutrients from inside the egg . Most live - bearing fish, amphibians or reptiles are actually ovoviviparous . Examples include the reptile Anguis fragilis, the sea horse (where zygotes are retained in the male's ventral "marsupium"), and the frogs Rhinoderma darwinii (where the eggs develop in the vocal sac) and Rheobatrachus (where the eggs develop in the stomach). </Li> <Li> Histotrophic viviparity means embryos develop in the female's oviducts but obtain nutrients by consuming other ova, zygotes or sibling embryos (oophagy or adelphophagy). This intra-uterine cannibalism occurs in some sharks and in the black salamander Salamandra atra . Marsupials excrete a "uterine milk" supplementing the nourishment from the yolk sak . </Li> <Li> Hemotrophic viviparity is where nutrients are provided from the female's blood through a designated organ . This most commonly occurs through a placenta, found in most mammals . Similar structures are found in some sharks and in the lizard Pseudomoia pagenstecheri . In some hylid frogs, the embryo is fed by the mother through specialized gills . </Li> </Ul> <Li> Ovuliparity means the female spawns unfertilized eggs (ova), which must then be externally fertilised . Ovuliparity is typical of bony fish, anurans, echinoderms, bivalves and cnidarians . Most aquatic organisms are ovuliparous . The term is derived from the diminiutive meaning "little egg". </Li>

Where are insect eggs most commonly found on a body