sponge participate in external fertilization where the ova is released. Expulsion At some point, the growing egg or offspring must be expelled. There are several possible modes of reproduction. These are traditionally classified as follows: Oviparity, as in most invertebrates and reptiles, monotremes, dinosaurs and all birds which lay eggs that continue to develop after being laid, and hatch later. Viviparity, as in almost all mammals (such as whales, kangaroos and humans) which bear their young live. The developing young spend proportionately more time within the female's reproductive tract. The young are later released to survive on their own, with varying amounts of help from the parent(s) of the species. Ovoviviparity, as in the garter snake, most vipers, and the Madagascar hissing cockroach, which have eggs (with shells) that hatch as they are laid, making it resemble live birth. Advantages to Internal Fertilization Internal fertilization allows for: Female mate choice, which gives the female the ability to choose her partner before and after mating. The female cannot do this with external fertilization because she may have limited control of who is fertilizing her eggs, and when they are being fertilized. Making a decision for the conditions of reproduction, like location and time. In external fertilization a female can only choose the time in which she releases her eggs, but not when they are fertilized. This is similar, in ways, to cryptic female choice. Egg protection on dry land. While oviparous animals either have a jelly like ovum or a hard shell enclosing their egg, internally fertilizing animals grow their eggs and offspring inside themselves. This offers protection from predators and from dehydration on land. This allows for a higher chance of survival when there is a regulated temperature and protected area within the mother. Disadvantages to Internal Fertilization Gestation can and will add additional risks for the mother. The additional risks from gestation come from extra energy demands. Along with internal fertilization comes sexual reproduction, in most cases. Sexual reproduction comes with some risks as well. The risks with sexual reproduction are with intercourse, it is infrequent and only works well during peak fertility. While animals which externally fertilize are able to release egg and sperm, usually into the water, not needing a specific partner to reproduce. Fewer offspring are produced through internal fertilization in comparison to external fertilization. This is both because the mother cannot hold and grow as