head
Frog's head is flat, slightly triangular and its snout is slightly sharp. The mouth is wide and horizontal, and consists of upper and lower jaws. There are a pair of nostrils at the front end of the back of the maxilla, and there are alars at the outer edge of the external nostrils. Eyes are large and prominent, born on the left and right sides of the head, with upper and lower eyelids; There is a translucent transient membrane on the inner side of the lower eyelid. When the eyelids are closed, there is a round eardrum behind each eye (toad's eardrum is smaller. There are a pair of oval protrusions on the back and upper part of the eye and tympanic membrane, which are called retroauricular glands. The male frog has a layer of light brown membrane pleats on the inside and back of the corner of his mouth, which is a sound bag and will swell into a bubble when singing.
tree trunk
Behind the eardrum is the trunk. The frog's trunk is short and wide, and there is a small hole between the legs at the back end of the trunk, which is a cloacal hole.
Arms and legs
The forelimb is short and consists of five parts: upper arm, forearm, wrist, palm and fingers. Four fingers, no webbed fingers. In the breeding season, the male frog has an enlarged protuberance on the inside of the root of the first finger, which is called a marriage tumor and is used to hold the right. The hind limbs are long and developed, which are divided into five parts: thigh, tibia, tarsal bone, metatarsal bone and toe. Five toes with a web in the middle. There is a hard keratinization distance on the inside of the first toe.
Frog preys
Frog's tongue is different from human's. The root of the tongue grows on the top of the bottom of the mouth, but it extends into the mouth. It is long and wide, and its front end is forked like a polyp, covered with mucus. When an insect flies, it quickly sticks out its tongue, sticks to the insect and rolls it into its mouth.
evolution of species
With the continuous evolution of frogs, there are all kinds of frightening and grotesque frogs. Some frogs secrete venom to guard against natural enemies. A tree frog that lives in the Amazon rain forest is called poison dart frog. Its secretion is used by local Indians to make poison arrows and seal their throats with blood.
Frog ancestors lived in water at first, but later, due to the change of living environment, some rivers and lakes became land, and frog ancestors gradually developed from water to land with the change of environment. The change of living environment forces frog ancestors to make corresponding "adjustments" to their body organs to adapt to the change of environment. Some species that can adapt to land life survived. The moving organ has changed from a tail that swims in water to limbs that can move on land and in water, and the respiratory organ has changed from gills to lungs. Frog's ancestors did not completely change from aquatic to terrestrial, so they showed up in the development of frog larvae. The difference between tadpoles and frogs is the legacy left by their ancestors.