1 . SOCIAL SECURITY FOR MIGRANT WORKERS - INVALIDITY INSURANCE - PENSIONS PAYABLE UNDER THE LEGISLATION OF SEVERAL MEMBER STATES - FAMILY ALLOWANCES - DETERMINATION - PAYMENT - SYSTEM ( REGULATION NO 3 , ARTICLE 42 ( 2 ) AS AMENDED BY ARTICLE 1 OF REGULATION NO 1/64 OF THE COUNCIL ) 2 . SOCIAL SECURITY FOR MIGRANT WORKERS - RIGHTS ACQUIRED UNDER THE LEGISLATION OF ONLY ONE MEMBER STATE - GUARANTEE - MEASURES OF THE COUNCIL PURSUANT TO ARTICLE 51 OF THE EEC TREATY - CHOICE - MEANS JUSTIFIED - INEQUALITIES BETWEEN WORKERS DUE TO DISPARITIES BETWEEN THE NATIONAL SCHEMES IN QUESTION - POSSIBILITY - ACCEPTABILITY