several  years;  dozens  of  experiments  take  place  simulta- neously,  often  involving  hundreds  of  fish.  Kallman  never became  overwhelmed  by  this  orderly  mass  of  extremely complicated, interrelated information. His complete famil- iarity stood him in good stead when, in April 1959, Gordon suddenly  died.  Less  than  a  year  later,  Kallman  was  put  in charge of the laboratory, which continued to function with little  noticeable  change.  Unquestionably,  Kallman  knew more about what was going on in the New York Zoological Society’s fish genetics laboratory than did anyone else. He had become “the man of the moment,” and he continued to lead this premier laboratory for the next 33 years. While  overseeing  all  the  laboratory’s  daily  operations, including  shipping  live  fish  to  investigators  in  other  insti- tutions, Kallman carried on his own vigorous research pro- gram.  In  all,  he  published  at  least  70  substantive  papers, amounting to 1164 pages. A dozen of his articles concerned the unique sex chromosomes of the platyfish (Xiphophorus maculatus), which has 3 kinds instead of the usual 2: XY and YY males, and XX, WX, and WY females. The WW female has  not  been  found  in  the  wild,  but  was  produced  in  the laboratory.  In  a  most  impressive  review,  Kallman  (1984) marshals the evidence for a theory of how this system of sex differentiation evolved and argues convincingly against the idea that it simply results from the primitiveness of piscine chromosomes. However, the existence of atypical sex deter- mination  complicates  the  matter  because  individuals  that exhibit normal sexual development and function can pos- sess the sex chromosomes of the opposite sex: XY and YY females and XX, WX, WY, and even WW males. Kallman showed that the interactions of the sex chromosomes with specific  autosomal  factors  played  important  roles  in  such often highly predictable events. He also convincingly laid to rest  the  phenomenon  of  sex  reversal  in  swordtails  from functional female to functional male. In  1973,  Kallman,  Martin  P.  Schreibman,  and  Valerie Borkoski  announced  the  discovery  of  a  sex-linked  gene  in Xiphophorus  maculatus,   the  alleles  of  which  determined when  the  pituitary  gonadotrops  were  activated  and,  thus, the onset of sexual maturation of males and females (Kall- man  et  al.,  1973).  Inasmuch  as  the  release  of  androgens terminates growth, early-maturing males were significantly smaller  than  late-maturing  ones.  So  far,  9  different  alleles have  been  identified  in  this  species  (Kallman,  1989).  The polymorphism of this gene differed in each of the 10 species of  Xiphophorus  that Kallman studied. Moreover, it was as- sociated  with  such  phenomena  as  sexually  active  dwarf males or giant ones that never matured. Some species had 2 genotypes  of  differently  sized  males,  which  exhibited  very different mating behavior patterns. Kallman’s discovery of this sex-linked gene added a new dimension to our under- standing of fish growth. The color patterns of the common platyfish have been studied intensively by fish culturists, geneticists, evolution- ists,  pigment-cell  biologists,  and  cancer  researchers.  Un- doubtedly, Kallman’s contributions to our understanding of the  inheritance  of  coloration  and  pigmentary  neoplasia  in Xiphophorus  provided  basic  data  on  which  many  of  these Professor Klaus D. Kallman, Director of the Xiphophorus Genetic Stock Center. This photograph was taken at the Osborn Laboratories of Marine Research, New York Aquarium, Brooklyn, New York, sometime in the late 1970s. (Reproduced with permission from the Wildlife Conservation Society.) S4 James W. Atz and Steven Kazianis Next >>