Asymmetrical testicular weights in mammals, birds, reptiles and amphibia.

The testes of different classes of animals (mammals, birds, reptiles and amphibia) were weighed. Some species showed inconsistent left-right asymmetric testicular weights, while other species (including amphibians, reptiles, some birds and some mammals) showed consistent asymmetry in their weights. In rodents, for example, five strains of mice consistently exhibited asymmetrical testes, with the right testis always being heavier than the left. In contrast, another strain of mice showed inconsistent bilateral asymmetry of the testes.