[blasto- + -sphere]blasto- is a combining form meaning “bud, sprout,” “embryo,” “formative cells or cell layer,”used in the formation of compound words. Other words that use the affix blasto- include: blastocyst, blastogenesis, blastopore, blastospore, blastostyle; -sphere is a combining form of sphere (planisphere); the form has a special use in the names of the layers of gases and the like surroundingthe earth and other celestial bodies (ionosphere). Other words that use the affix -sphere include: centrosphere, exosphere, ionosphere, lithosphere, mesosphere