Classification Of Eggs Based Upon Amount Of Yolk

1. Classification Of Eggs Based Upon Amount Of Yolk Egg Type Representative Organisms a) Alecithal - Almost without yolk. Placental mammals b) Microlecithal - Small amount of yolk. Echinoderms, amphioxus, marsupials c) Mesolecithal - Moderate amount of yolk. Lung-fishes, frogs, and toads. d) Macrolecithal - Very large amounts of yolk. Sharks, bony fishes, reptiles, birds, insects.

2. Classification Of Eggs Based Upon Distribution Of Yolk • a.) Isolecithal or Homolecithal - Yolk is evenly distributed. Occurs in the alecithal and microlecithal eggs of echinoderms, amphioxus, marsupials, and other mammals. • b) Telotecithal - Yolk is concentrated on one end of the egg, the vegetal hemi-sphere, with the cytoplasm plus the nucleus concentrated the at other end, the animal hemisphere. Occurs in the mesolecithal and macrolecithal eggs of frogs, toads, birds, reptiles etc. • c.) Centrolecithal - Yolk is in the center of the egg, with cytoplasm around it. Example: Insect eggs

3. Endolecithal and Ectolecithal Eggs