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