INTERNAL DEVELOPMENT Involves the growth of the embryo INSIDE the body of the parent

FERTILIZATION Internal development must have INTERNAL fertilization The gametes unite in the moist reproductive tract of the female -The eggs have very little yolk

PLACENTAL MAMMALS An organ called the placenta is developed from MATERNAL and EMBRYONIC tissue

PLACENTA- The placenta is used for the exchange of OXYGEN, NUTRIENTS, and WASTES between mother and embryo Exchange is accomplished by DIFFUSION between the blood of the mother and the blood of the embryo There is no direct connection to blood

Exchange

Examples Humans and most other mammals are placental mammals- Then, there’s those weird ones 

MARSUPIALS Have PARTIAL internal development After fertilization, the embryo is RETAINED WITHIN THE MOTHER for a short period of time The embryo is born NOT WELL DEVELOPED

Marsupial embryos Crawl from the birth canal up to the POUCH Completes development within pouch, attached to a MAMMARY GLAND for nourishment

Examples Marsupials include kangaroos, opossums

GESTATION PERIOD Gestation period is THE LENGTH OF TIME OF INTERNAL DEVELOPMENT Examples:DOGS, 63 DAYS ELEPHANTS, 22 MONTHS

ADVANTAGES The advantage of internal fertilization is that there is a BETTER CHANCE THE EGG WILL BE FERTILIZED The advantage of internal development is there is A BETTER CHANCE OF THE EMBRYO DEVELOPING INTO A LIVING ORGANISM

DISADVANTAGES The disadvantages of internal development are THE TIME INVESTED as well as A LIMIT TO THE NUMBER OF ORGANISMS THAT CAN DEVELOP AT ONE TIME