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By embryo we mean in the sense of up to the 8th week postfertilization (over 7 and under 8 weeks), we treat fetus as a separate stage.

Starts at day 1 post-fertilization, beginning of the first week.

Usually starts between day 2 and day 3 post-fertilization.

The blastula follows the morula and precedes the gastrula in the developmental sequence.

Usually starts between day 4 and day 5 post-fertilization.

Usually starts between day 5 and day 6 post-fertilization.

Usually starts between day 7 and day 12 post-fertilization, beginning of the second week.

Usually starts between day 13 and day 15 post-fertilization.

This stage starts the emergence of the central nervous system.

Usually starts between day 15 and day 17 post-fertilization, beginning of the third week.

Usually starts between day 17 and day 19 post-fertilization.

Usually starts between day 19 and day 21 post-fertilization.

Usually starts between day 22 and day 23 post-fertilization, beginning of the fourth week.

Usually starts between day 23 and day 26 post-fertilization.

Usually starts between day 26 and day 30 post-fertilization.

Usually starts between day 28 and day 32 post-fertilization, beginning of the fifth week.

Usually starts between day 31 and day 35 post-fertilization.

Usually starts between day 35 and day 38 post-fertilization.

Usually starts between day 37 and day 42 post-fertilization, beginning of the sixth week.

Usually starts between day 42 and day 44 post-fertilization.

Usually starts between day 44 and day 48 post-fertilization, beginning of the seventh week.

Usually starts between day 48 and day 51 post-fertilization.

Usually starts between day 51 and day 53 post-fertilization, beginning of the eighth week.

Usually starts between day 53 and day 54 post-fertilization.

Usually starts between day 54 and day 56 post-fertilization.

Usually starts between day 56 and day 60 post-fertilization.

Prenatal development is a continuum, with no clear defining feature distinguishing an embryo from a fetus. The use of the term "fetus" generally implies that a mammalian embryo has developed to the point of being recognizable as belonging to its own species, though the point at which this occurs is subjective. [Wikipedia:Fetus]

External genitalia begin to distinguish themselves as either male or female. Eyelids are completely closed, and vocal ligaments appear (see http://ehd.org/resources_bpd_documentation_english.php).

The fingernails and toenails begin to develop and unique fingerprints appear. Ossification is underway in most bones (see http://ehd.org/resources_bpd_documentation_english.php).

The nose and lips are completely formed, and external genitalia can be distinguished as male or female (see http://ehd.org/resources_bpd_documentation_english.php).

Upper limb length has nearly reached its final proportion to body size (see http://ehd.org/resources_bpd_documentation_english.php). The assignation of this week to the fourth or third LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).

The assignation of this week to the fifth or fourth LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).

The cochlea has reached adult size within the fully developed inner ear (see http://ehd.org/resources_bpd_documentation_english.php). The assignation of this week to the sixth or fifth LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).

The lungs gain some ability to breathe air. This stage is considered the age of viability because survival outside the womb becomes possible for some fetuses (see http://ehd.org/resources_bpd_documentation_english.php).

The eyelids reopen (see http://ehd.org/resources_bpd_documentation_english.php).

The assignation of this week to the seventh or sixth LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).

The assignation of this week to the eighth or seventh LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).

The assignation of this week to the eighth or ninth LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).

The assignation of this week to the ninth or tenth LMP month is debatable (see http://en.wikipedia.org/wiki/File:Prenatal_development_table.svg).