Gratuity Related Question For Contract Labour

Here is an interesting case regarding gratuity should be payable for a contract labour or not.
A principal employer X renews only rate contracts for a contractor B for supply labour.
Contractor B has no written contract with any of his worker and they[B] have monthly payment on daily wages basis.
Some worker of Contractor B attends his duty rarely [say, 10 days in a month] but working under 'B' for last 8 years.
Now, he wants to go out.
Should he be entitled for gratuity ? and if yes - what should be the basis of calculation.
The name of 'X' and 'B' is kept confidentiontial for the security of Contractor 'B' but they are really in atrouble - Pl. anyone in W.Bengal guide with a solution.
Thanks,
Krishnendu

Since the principal employer has no legal relationship with the worker of contractor the principal employer should not be in picture at all.
The contractor has hired employees and has been paying wages to his employees. If one of his employees leaves after 8 years of service, it is his responsibility to pay gratuity to that worker and he is suppose to pay it. Now whether the employee is eligible to gratuity or not is to be decided after verifying his service. Inorder to be eligible to gratuity one has to be in continuous service for five years. Now in order to constitute continuous service one has to work at least for 240 days in each year. In this case, if the employee has the habit of working for 10 days in a month, then it is doubtful whether he would attain continuous service. Please verify whether he use to work for 240 days in each year.
Regards,
Madhu.T.K