What defines internal fertilization?

Internal fertilization is defined by the process in which sperm is introduced directly into the female reproductive tract. This method of fertilization typically occurs in terrestrial or some aquatic organisms, allowing for fertilization to take place inside the female's body, which often provides a more protected environment for the developing embryo.

In contrast, releasing gametes into the water refers to external fertilization, where egg and sperm meet outside the body. The mention that internal fertilization occurs only in aquatic species is inaccurate, as it primarily happens in terrestrial species, such as mammals and reptiles. Additionally, the assertion that fertilization takes place outside the female body is characteristic of external fertilization rather than internal fertilization. Thus, the introduction of sperm into the female reproductive tract is the key feature that defines internal fertilization.