an egg whose cytoplasm contains a large quantity of yolk unevenly distributed. There is comparatively little yolk and a great deal of cytoplasm in the upper (generative) pole of the egg and much yolk and little cytoplasm in the lower (vegetative) pole. The nucleus is shifted to the generative pole. Telolecithal eggs are characteristic of several invertebrates, for example, some crustaceans and cephalopod and gastropod mollusks, and of most vertebrates, including fish, amphibians, reptiles, birds, and monotremes.