1. Othenio Abel, ?Die Festgabe der ?Palaeobiologica,?? Palaeobiologica, 1 (1928), 1?8.
2. 1912, p. 117. A chronological bibliography of Dollo's work on irreversibility is presented at the close of this article. Citations herein are by date and refer to these works.
3. 1922, p. 219.
4. 1922, p. 223.
5. 1912, p. 140.