1. The layer of cells that develops on the surface of the yolk in an avian or reptilian egg and gives rise to the germinal disk from which the embryo develops.
2. The layer of cells formed by the cleavage of a fertilized mammalian egg. It later divides into the three germ layers from which the embryo develops.
blas′to·der·matic (-dər-mătĭk), blas′to·dermic adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.