Reproduction In Animals (1957)

[Music] a mother dog and puppies one of the most common examples of animal reproduction we might see the puppies are dependent on their mother just as these baby rabbits are dependent on their mother baby birds too are dependent upon the parent bird during the early days of their lives some animals such as these tadpoles can get along without parental care in general amphibians and other lower forms of animal life require little or no parental care if we look at a sample of pond water under a microscope we'll probably find amoeba one of the simplest animals it is also an example of the simplest kind of reproduction in animals this large amoeba is reproducing asexually the single cell is separating by simple fishing into two cells these slowly move apart until the parent cell becomes two two separate cells two individuals Hydra a simple multicellular animal can also reproduce asexually a bud develops on the parent and eventually breaks off to become a separate individual in the more complex animals reproduction is more complex these are eggs laid by a female frog here are the beginnings of dozens of frogs new two individuals each one begins with a single fertilized egg seen here highly magnified to produce such an egg cell two parents are necessary the male parent produces special reproductive cells called sperm cells these are living sperm cells of the Frog these are sperm cells of a mouse the sperm cells of the male parent and egg cell of the female are brought together by a process we call mating in some animals mating includes an active courtship such as the male fish is carrying on reproduction begins when after mating sperm cells and egg cells unite this is called Fertilization in the Frog it takes place outside the field female's body a fertilized egg is called a zygote the first stage of growth begins when this single cell becomes two cells by speeding the action with the camera we can watch the division taking place first into two cells each will form half of the tadpole then the two cells divide into four cells the four cells divide div into eight cells the cells continue to multiply 8 16 32 64 128 and so on all cells of the same animal gradually thousands of cells begin to form a single embryo the tiny living body of a new frog here we can see the beginnings of the head on the right each growing living embryo is encased within a protective jellylike covering after a week or two the tiny embryos break out of their jelly-like coverings they hatch we followed one example of reproduction in an egg laying animal the Frog other animals including Birds also reproduce by laying eggs of course two parents are necessary in birds and in insects fertilization takes place place inside the female's body after mating many insects such as this Moth lay eggs on Twigs or leaves where they are left without further care Turtles and many other reptils are egg layers too the female Turtle usually lays her eggs in sand where they are left to hatch by the warm sun although the shell of a turtle egg is soft it still provides protection for the developing embryo within it the eggs of birds like this familiar chicken egg are hard within this protective shell is the living chick embryo in a similar way the turtle embryo develops within the turtle egg and so in the egg laying animal Birds amphibians many reptils and others the embryo develops in an egg outside of the mother's body in mammals fertilization takes place inside the female's body the embryo develops inside the body of the pregnant female here are two mouse embryos in a late stage of development do you see the similarity between this Mouse embryo and the chick embryo we saw in early stages of development embryos of different animals show even more similarities so the embryo grows until it is large enough to be born being born is a vital step in the process of reproduction and it takes place in a number of ways when the young emerge from eggs outside the mother's body we call this birth hatching the hatching of birds is probably our most familiar example of this kind of birth let's watch the process as we do we might think of a simple definition of reproduction the creation of a new individual from one or two parents and here is our new individual a baby robin this is hatching 2 the hatching of tadpoles most fish are born in a similar way here is an insect hatching from one of the insect eggs we saw the turtle eggs left in the warm sand are hatching too hatching from eggs is a very common form of birth in animals in most mammals the young emerge alive from the the mother's body watch the mouse carefully we are going to see the actual birth of a mouse at Birth the young are quite helpless a finger gives us some idea of their size now the mice about half grown are beginning to resemble the parent they are still dependent on the mother's milk for food some birds too must feed their young other young birds such as chicks can eat and run about soon after being born the young of turtles and other reptiles are able to take care of themselves as soon as they are born young frogs and other amphibians also get along by themselves most Bab fish too Need No Parental care in mammals the period of dependence on the mother or infancy lasts longer than for other animals for example it takes 6 to 7 weeks after birth for a baby mouse to mature young dogs have a longer period of infancy and also a longer period of growing to maturity human babies have the longest Peri period of dependence upon their parents the years of infancy and gradual growth to maturity are stages in the development of an individual a new individual that is the result of reproduction we saw that reproduction in the lower animals is simple fishing is one method budding is another both are asexual forms of reproduction sexual reproduction in the higher forms of animal life takes place when the egg cell of the female is fertilized by a sperm cell of the male fertilization may take place outside the female's body for example as with many amphibians or within the body as with insects for example after thousands of cell divisions the fertilized egg grows into an embryo sometimes the embryo develops within a shell outside of the mother's body sometimes the embryo develops inside the mother's body and is born alive although the process of reproduction varies greatly among animals the end result is always the same the creation of a new individual h