A. Labour Law — Employees' State Insurance Act, 1948 — S. 4(1) — Applicability to casual workmen — Casual workmen of contractor engaged by principal employer — Contribution in respect of them payable although contract completed much prior to demand for such contribution made by Corporation — Held, it was duty of principal employer to get necessary details of workmen employed by contractor at commencement of contract since primary responsibility of payment of contribution is on principal employer — On admitted fact that principal employer had engaged contractor to execute work, it was also duty of principal employer to get temporary identity certificates issued to workmen as per provisions of 1950 Regulations and to pay contribution as required by S. 40 — Since principal employer failed in its obligation, it cannot be heard to say that workers are unidentifiable — It was within exclusive knowledge of principal employer as to how many workers were employed by its contractor — If principal employer failed to get details of workmen employed by contractor, it has only itself to thank for its default — Since workmen in fact were engaged by contractor to execute work in question and principal employer had failed to pay contribution, appellant-Corporation was entitled to demand contribution although both contribution period and corresponding benefit period had expired — Scheme under Act for insuring workmen for conferring on them benefits in case of accident, disablement, sickness, maternity etc. is distinct from contract of insurance in general — Under 1948 Act, scheme is more akin to group insurance — Contribution paid entitles workman insured to benefit under 1948 Act — However, he does not get any part of contribution back if during benefit period, he does not qualify for any of benefits — Contribution made by him and by his employer is credited to insurance fund created under 1948 Act and it becomes available for others or for himself, during other benefit periods, if he continues in employment — What is more, there is no relation between contribution made and benefit availed of — Contribution is uniform for all workmen and is a percentage of wages earned by them — It has no relation to risks against which workman stands statutorily insured — It is for this reason that S. 4(1) envisages automatic obligation to pay contribution once factory or establishment is covered by 1948 Act, and obligation to pay contribution commences from date of application of 1948 Act to such factory or establishment — Obligation ceases only when 1948 Act ceases to apply to factory/establishment — Obligation to make contribution does not depend upon whether particular employee or employees cease to be employee/employees after contribution period and benefit period expire — Labour Law — Employees' State Insurance Act, 1948 — S. 4(1) — Applicability to casual workmen — Casual workmen of contractor engaged by principal employer — Contribution in respect of them payable although contract completed much prior to demand for such contribution made by Corporation — Held, it was duty of principal employer to get necessary details of workmen employed by contractor at commencement of contract since primary responsibility of payment of contribution is on principal employer — On admitted fact that principal employer had engaged contractor to execute work, it was also duty of principal employer to get temporary identity certificates issued to workmen as per provisions of 1950 Regulations and to pay contribution as required by S. 40 — Since principal employer failed in its obligation, it cannot be heard to say that workers are unidentifiable — It was within exclusive knowledge of principal employer as to how many workers were employed by its contractor — If principal employer failed to get details of workmen employed by contractor, it has only itself to thank for its default — Since workmen in fact were engaged by contractor to execute work in question and principal employer had failed to pay contribution, appellant-Corporation was entitled to demand contribution although both contribution period and corresponding benefit period had expired — Scheme under Act for insuring workmen for conferring on them benefits in case of accident, disablement, sickness, maternity etc. is distinct from contract of insurance in general — Under 1948 Act, scheme is more akin to group insurance — Contribution paid entitles workman insured to benefit under 1948 Act — However, he does not get any part of contribution back if during benefit period, he does not qualify for any of benefits — Contribution made by him and by his employer is credited to insurance fund created under 1948 Act and it becomes available for others or for himself, during other benefit periods, if he continues in employment — What is more, there is no relation between contribution made and benefit availed of — Contribution is uniform for all workmen and is a percentage of wages earned by them — It has no relation to risks against which workman stands statutorily insured — It is for this reason that S. 4(1) envisages automatic obligation to pay contribution once factory or establishment is covered by 1948 Act, and obligation to pay contribution