Evidence of land animals carrying internal vertilisation?

Internal fertilisation is a reproductive strategy in which the male gametes (sperm) are introduced directly into the female reproductive tract, where they can encounter and fertilise the female gametes (eggs) within the body of the female. Land animals, including those that carry out internal fertilisation, have various adaptations to facilitate this process and ensure successful reproduction on land. Here's evidence of land animals with adaptations for internal fertilisation:

1. Snails and Slugs (Gastropods):

- Many species of land snails and slugs have male reproductive structures called penises, which they insert into the female's reproductive system to deliver sperm during mating.

- After mating, some species practice sperm storage within the female reproductive tract, allowing fertilisation to occur when conditions are favourable for egg development.

2. Invertebrates: Insects, Spiders, Scorpions:

- Among insects, spiders, and scorpions, internal fertilisation is common. Male spiders deposit sperm into specialised structures on their pedipalps, which they then insert into the female's reproductive opening during mating.

- In scorpions, the male uses specialised appendages called "gonopods" to transfer sperm to the female during mating, ensuring internal fertilisation.

3. Reptiles: Snakes, Lizards, Crocodilians:

- Most reptiles, including snakes, lizards, and crocodilians, exhibit internal fertilisation. Male snakes have hemipenes, which are paired erectile organs used to deliver sperm into the female's cloaca during mating.

- Lizards and crocodilians also possess specialised reproductive structures for internal fertilisation.

4. Amphibians: Frogs and Salamanders:

- Frogs and other amphibians rely on internal fertilisation. Male frogs have specialised thumb pads called "nuptial pads" that help grasp the female during amplexus, the mating position during which the male releases sperm over the externally laid eggs, allowing for internal fertilisation to take place.

5. Mammals:

- Mammals are well-known for their internal fertilisation methods. During reproduction, male mammals have an intromittent organ called the penis, which is inserted into the female's reproductive tract, allowing the transfer of sperm into the female's body for internal fertilisation.

- Mammals often exhibit complex reproductive behaviours and physiological adaptations to support embryo development within the female's body or external pouches, depending on the species.

These examples demonstrate that various land animals have evolved adaptations for internal fertilisation, enabling them to successfully reproduce on land, away from aquatic environments. These adaptations ensure that sperm are delivered directly into the female's reproductive tract, increasing the chances of fertilisation and facilitating embryo development within the female or the external environment, as in the case of some reptiles and amphibians.