What do the developmentalists mean when they say that the embryonic period is the most critical period of prenatal development?

Conception occurs when a sperm fertilizes an egg and forms a zygote, which begins as a one-cell structure. The mother and father’s DNA is passed on to the child at the moment of conception. The genetic makeup and sex of the baby are set at this point. The germinal period (about 14 days in length) lasts from conception to implantation of the zygote (fertilized egg) in the lining of the uterus.

During the first week after conception, the zygote divides and multiplies, going from a one-cell structure to two cells, then four cells, then eight cells, and so on. The process of cell division is called mitosis. After the fourth division, differentiation of the cells begins to occur as well. Differentiated cells become more specialized, forming different organs and body parts.  After 5 days of mitosis, there are 100 cells, and after 9 months there are billions of cells. Mitosis is a fragile process, and fewer than one-half of all zygotes survive beyond the first two weeks (Hall, 2004).

After the zygote divides for about 7–10 days and has 150 cells, it travels down the fallopian tubes and implants itself in the lining of the uterus. It’s estimated that about 60 percent of natural conceptions fail to implant in the uterus. The rate is higher for in vitro conceptions. Once the zygote attaches to the uterus, the next stage begins.

Explanation:

my hamster died and my second hamster i got after that one died as well. i also lost two birds named rainbow and kiwi, (they didn't die, they flew off and escaped). i lost a cat named omi, and a dog named snoopie. the best way i got over it is, paying my respects, and just thinking that they were in a happy place. as well as just remembering but not thinking about it all the time, just do fun activities and try not to think about it too much. hope you feel better. i'm sorry about your loss. : (