Polymorphism of the middle wavelength cone in two species of South American monkey: Cebus apella and Callicebus moloch.

The spectral sensitivity of the middle wavelength cone was measured in two species of South American monkey, Cebus apella and Callicebus moloch, using electroretinogram (ERG) flicker photometry. Both of these species were found to have a polymorphism of the middle wavelength cone. Eight male Cebus monkeys each had only a single type of middle wavelength cone having lambda max values of either 550 or 562 nm. Eight Callicebus monkeys (7 male, 1 female) showed a similar polymorphism of the middle wavelength cone (lambda max = 549 or 561 nm). A single female of this latter species had two types of middle wavelength cone. The cone polymorphisms of these species appear very similar to that previously described for the squirrel monkey (Saimiri sciureus).