11/5/2022 0 Comments Fate of blastopore birds![]() ![]() Eggs with little yolk, such as those of most marine invertebrates, divide ompletely (holoblastic) and usually have indirect development with a larval stage terposed between the embryo and adult. Cleavage is greatly influenced by the quantity and distribution of olk in the egg. of their own species, and all have eveloped devices to prevent polyspermy.ĭuring cleavage the embryo divides rapidly and usually synchronously, producing a ulticellular blastula. Many eggs release chemical sperm attractants, most have surface ceptors that recognize and bind only with sperm. The sperm is a highly condensed haploid nucleus provided with a comotory flagellum. Both sperm and egg have evolved devices to promote ficient fertilization. ertilization of an egg by a sperm restores the diploid number of chromosomes and tivates the egg for development. Pearance of new structures that arise as the products of antecedent development. The early preformation concept of development gave way in the eighteenth – ntury to the theory of epigenesis, which holds that development is the progressive Answer of Question of Descriptive Embryologyĭevelopmental biology is concerned with the emergence of order and complexity ring the development of a new individual from a fertilized egg, and with the control of ![]()
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