No products or materials specified in the regulations in this part shall be imported unless there be shown upon the commercial invoice, or in some other manner satisfactory to the Deputy Administrator, Veterinary Services, the name of the region of origin of such product or material: Provided, That the region of origin shall be construed to mean (a) in the case of an animal byproduct, the region in which such product was taken from an animal or animals, and (b) in the case of other materials, the region in which such materials were produced.