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animals with two cellular body wall layers: the ectoderm and endoderm.
a complex organic substance needed by the body in small amounts for normal growth and...
the gamete-producing phase that produces the zygote from which the sporophyte emerges.
an international agreement to phase out the use of CFCs, signed by 49 countries in Montreal,...
the internal supporting framework made of cartilage and/or bone. This type of skeleton occurs in...