The first animal group to possess a complete digestive system is .........

The $Aschelminthes$ are commonly called roundworms because:

Which of the following statements are correct about the life cycle of $Ascaris \; lumbricoides$?
$(A)$. Infective agent - Embryonated egg with $II$ Juvenile
$(B)$. Fertilised eggs containing the unsegmented ovum are passed with faeces
$(C)$. Four moultings of the larva occur: two outside in soil within the egg-shell, one in lungs and one in intestine
$(D)$. Site of location of worm - small intestine.

In the given figure,what does the part labeled '$a$' represent?

Female $Ascaris$ is differentiable from male in

The embryonated egg of $Ascaris$ is: