Question

Eric is observing various types of eggs and trying to correlate them with the mode of fertilization. One of the eggs has a calcareous shell with a large amount of yolk. Another is wet with a moderate amount of yolk and with many coatings of jelly above it. What could be the mode of fertilization of the animals to which they belong

Answer 1

The calcareous shelled egg could have been conceived through internal fertilization, and the jellied egg through external fertilization. Sperm wouldn't be able to pass through the calcareous shell if it were external, so thus the egg for it must have been fertilized before the shell formed. Also, because protection for the unfertilized egg is paramount, most animals who lay calcareous egg use internal fertilization. With the jellied egg, sperm can slowly pass through a jellied layer to fertilize the egg, and when the egg is fertilized, the jelly can harden into a coat to protect the egg.