How do we determine which is an animal pole and which is a vegetal pole in a zygote?
My professor said that the zygote can be divided into two hemispheres, vegetal and animal poles. The hemisphere with yolk is the vegetal pole and the one without is the animal pole.
But I couldn't find an authentic book that I have access to saying anything about the polarity of the zygote. However I stumbled upon this paragraph from Objective Zoology and I'm not sure if it's right.
Zygote or egg of frog is spherical and measures about 1.6mm in diameter. The upper half of the zygote is black (pigmented) and contains nucleus and cytoplasm. The lower part of the zygote is white or light yellow in colour and contains the reserve food in the form of yolk. The upper pigmented part is called the animal pole and the lower part vegetal pole.