Describe the structure and life cycle of Ascaris lumbricoides with the help of neat and labelled diagram.

Structure of Ascaris lumbricoides:
a) Its common name is round worm
b) Sexes are separate and the sexual dimorphism is distinct.
c) The body of both males and females is elongated and cylindrical.
d) Mouth: Mouth is present at the extreme anterior end and is surrounded by chitinous
lips.
e) Excretory pore : Close to the mouth, mid ventrally there is a small aperture called excretory pore.
Male :
a) It has a curved posterior end with cloaca.
b) The posterior end possess a pair of equal sized chitinous pineal spicules or pineal setae. They are useful for transfer the sperms during copulation.
Female :
a) It has a straight posterior end with anus.
b) The female genital pore is present mid ventrally at about one third the length from mouth.
Life history : It is a monogenetic parasite.
a) Copulation : Copulation takes place in the small intestine of man.
b) Mammillated eggs : After copulation ,the female releases two lakh eggs per day. Each egg is surrounded by a protein coat with rippled surface. Such eggs are mammillated eggs.
c) Development of egg into larva : The eggs come out along with faecal matter. In the moist soil development takes place inside the egg so that 1at stage rhabditiform larva is produced.
d) 2nd Stage larva : 1st stage larva undergoes moulting and becomes the 2nd stage rhabditiform larva. It is the infective stage to man.
e) Entry into man : Infective stages reach the alimentary canal of man through contaminated food and water.
f) Extra intestinal migration : In the small intestine, the shell gets dissolved so that the 2^nd stage larva is released. Now it undergoes extra intestinal migration.
First it reaches the liver, then heart and finally lungs. In the alveoli of lungs it undergoes 2^nd moulting to produce the 3^rd stage larva. 
It undergoes 3^rd moulting so that 4^th stage larva is produced in the alveoli.
It leaves the alveoli and reaches the small intestine again through trachea, larynx, pharynx, oesophagus and stomach.
In the small intestine the larva undergoes 4^th & final moulting to become an adult.
Pathogenicity : The disease caused by Ascaris lumbricoides is called 'Ascariasis'.