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http://journals.cambridge.org/action/displayAbstract?aid=40283
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GERALD H. JACOBS,
JESS F. DEEGAN
and JAY NEITZ
(1998).
Photopigment basis for dichromatic color vision in cows, goats, and sheep. Visual Neuroscience, 15
,
pp 581-584
doi:10.1017/S0952523898153154