studies rest (Kallman, 1975; Vielkind et al., 1989). In mak- ing these discoveries, he stood idyllically on the shoulders of his  mentor,  Myron  Gordon.  Furthermore,  on  a  practical level, many of us are indebted to him for generously sup- plying us with his fishes for our studies. Kallman’s interest in the platyfishes and swordtails has shifted  to  their  biogeography.  During  56  trips  to  Mexico and its neighboring countries, he has collected and observed more  of  these  fishes  in  their  natural  habitats  than  anyone else. In particular, he critically studied their distribution in relation to the history of the fresh waters they now inhabit and did in the past. He described at least five new species and witnessed the natural extinction of at least one (Rosen and  Kallman,  1969;  Rauchenberger  et  al.,  1990).  To  hear him expound on the subject, with map in hand or vista in view or in mind, is a rare treat. Kallman has traveled with and continues to assist dozens of researchers on collecting trips. Undoubtedly, every one of these individuals can attest to  his  extreme  determination,  planning,  incredible  perse- verance, and physical stamina. On numerous occasions, he has outperformed hikers 30 years his junior on treacherous slopes  within  cloud  and  rain  forests,  in  deep  valleys  and deserts.  Although  Kallman  now  is  Professor  Emeritus,  he continues to work with  Xiphophorus  and is preparing sev- eral manuscripts that will become prominent contributions to the scientific body of knowledge. Kallman  always  has  maintained  that  to  perform  well professionally, one must think of his or her occupation not simply as a job, but as an avocation. His avocation was, is, and always will be research with the  Xiphophorus  fishes. REFERENCES Kallman,  K.D.  (1970).  Genetics  of  tissue  transplantation  in  Tel- eostei.  Transplant Proc  2:263–271. Kallman,  K.D.  (1975).  The  platyfish,  Xiphophorus  maculatus.  In: Handbook  of  Genetics,  Vol.  4,  King,  R.C.  (ed.).  New  York,  N.Y.: Plenum Publishing Corporation, 81–132. Kallman,  K.D.  (1984).  A  new  look  at  sex  determination  in  poe- ciliid fishes. In:  Evolutionary Genetics of Fishes,  Turner, B.J. (ed.). New York, N.Y.: Plenum Publishing Corporation, 95–171. Kallman,  K.D.  (1989).  Genetic  control  of  size  at  maturity  in  Xi- phophorus. In: Ecology and Evolution of Livebearing Fishes (Poecili- idae), Meffe, G.K., and Snelson, F.F. Jr. (eds.). Englewood Cliffs, N.J.: Prentice Hall, 163–184. Kallman, K.D., Schreibman, M., and Borkoski, V. (1973). Genetic control of gonadotrop differentiation in the platyfish, Xiphophorus maculatus  (Poeciliidae).  Science  181:678–680. Rauchenberger,  M.,  Kallman,  K.D.,  and  Morizot,  D.C.  (1990). Monophyly  and  geography  of  the  Rio  Panuco  basin  swordtails (genus  Xiphophorus)  with  descriptions  of  four  new  species.  Am Mus Novitates  2975:1–41. Rosen,  D.E.,  and  Kallman,  K.D.  (1969).  A  new  fish  of  the  genus Xiphophorus  from  Guatemala,  with  remarks  on  the  taxonomy  of endemic forms.  Am Mus Novitates  2379:1–29. Vielkind, J.R., Kallman, K.D., and Morizot, D.C. (1989). Genetics of melanomas in Xiphophorus fishes. J Aquat Anim Health 1:69–77. Tribute to Klaus D. Kallman S5