1. Abelous, J. E., and Billard, G, 1896. Arch. Physiol. Norm. Pathol 47: 898.
2. Affanassiew, B, 1877. Arch. Mikroskop. Anat, p. 14. Aime, P., 1912a. Compt. Rend. Soc. Biol. (Paris) 72: 115.
3. Aime, P., 1912b. Compt. Rend. Soc. Biol. (Paris) 72: 889.
4. Allen, B. M., 1918. Anat. Rec. 14: 86.
5. Allen, B. M., 1920. J. Exptl. Zool. 30: 189.