| A | B |
|---|
| zygote | formed from the fusion of an egg with a sperm |
| embryo | a multicellular organism that is in the early stages of development |
| embryology | the study of the development of embryos |
| cleavage | an early series of cell divisions that occur without growth |
| morula | solid ball of cells |
| blastula | hollow ball of cells with fluid-filled center |
| blastocoel | the fluid-filled center of the blastula |
| gastrulation | cells on one side of blastula move inward to form two-layered embryo called the gastrula |
| gastrula | two, or three-layered embryo |
| germ layers | cell layers of the gastrula, which give rise to all tissues and organs |
| ectoderm | outer layer of gastrula-forms nervous system and skin |
| mesoderm | middle layer of gastrula-forms muscle, bone, blood vessels, blood, heart, reproductive system |
| endoderm | inner layer of gastrula-forms digestive, respiratory systems, liver, pancreas |
| development | the change of unspecialized cells into specialized cells, tissues, and organs |
| primitive gut | cavity within the gastrula/becomes digestive tract |
| coelom | body cavity lined by the mesoderm |
| protostome | the original dent of the balstopore becomes the anus |
| blastopore | a dent on one side of the balstula |
| deuterostome | the original dent of the balstopore remains the mouth anus |
| through gut | a tunnel through the animal with two openings |
