Table 1.

Some general differences between typical amniote rod and cone photoreceptors. (Opsin genes marked with an asterisk are not known to occur in snakes [10–12].)

	rods	cones
shape of outer segment	rod-like (cylindrical)	cone-like (distally tapering)
size of outer segment	longer	shorter
footpieces (synaptic pedicels)	small, oligosynaptic	large, polysynaptic
visual opsin genes expressed	rh1	rh2*, sws1, sws2*, lws
other phototransduction molecules	rod isoforms	cone isoforms
outer segment discs	individualized	partly continuous with outer plasma membrane
outer segment incisure	present	absent
oil droplets	absent	sometimes present (not in snakes)