Mammalian (especially placental) egg cells have very less yolk which should have been called microlecithal but as this yolk quantity is negligible the word alecithal has been especially found to explain this condition.

Understanding Human Eggs
Human eggs, or oocytes, are classified based on their yolk content. The classification is essential to understand embryonic development in humans and other species.
Types of Egg Yolks
- Alecithal Eggs: These eggs contain very little or no yolk. Human eggs fall into this category, making them alecithal. The minimal yolk allows for efficient nutrient absorption from the surrounding environment after fertilization.
- Microlecithal Eggs: These eggs have a small amount of yolk. Examples include some species of fish and amphibians that require a bit more nutritional support than human eggs.
- Mesolecithal Eggs: These contain moderate amounts of yolk. Typically found in certain amphibians, these eggs provide a balance of nutrients for developing embryos.
- Macrolecithal Eggs: These eggs are rich in yolk and are found in reptiles and birds. The substantial yolk supply supports the growth of the embryo until it can sustain itself.
Why Human Eggs are Alecithal
- Development Context: In humans, the embryo develops within the uterus, where it receives nutrients directly from the mother through the placenta. Therefore, large yolk reserves are unnecessary.
- Nutritional Support: The limited yolk in human eggs ensures that they are optimized for early development stages, relying on maternal resources for further growth.
In summary, human eggs are classified as alecithal due to their minimal yolk content, which is essential for efficient nutrient transfer during the early stages of embryonic development.