Question

Iris has
A. Rods
B. Cones
C. Radial and Circular Muscles
D. Both rods and cones

Answer 1

In humans and most warm-blooded creatures and birds, the iris is a meager, annular structure in the eye, liable for controlling the measurement and size of the student and consequently the measure of light arriving at the retina.

Complete answer:
The iris comprises two layers: the front pigmented fibrovascular layer known as stroma and, underneath the stroma, pigmented epithelial cells. The stroma is associated with a sphincter muscle (sphincter pupillae), which gets the understudy in a roundabout movement, and a lot of dilator muscles (dilator pupillae) which pull the iris radially to amplify the student, pulling it in folds.
The circle boundary sphincter choking muscle is the restricting muscle of the circle-span dilator muscle. The iris inward littler circle-periphery changes size while contracting or expanding. The iris external bigger circle-outline doesn't change size. The tightening muscle is situated on the iris internal littler circle-boundary.
The iris is partitioned into two significant locales:
The pupillary zone is the inward locale whose edge frames the limit of the student.
The ciliary zone is the remainder of the iris that reaches out to its beginning at the ciliary body.
The measure of light entering the eye is directed by the iris which controls the size of the understudy. Iris comprises two sorts of smooth muscles, round muscles, and spinal muscles. Round muscles are called sphincter pupillae and spiral muscles are called dilator pupillae. The size of the understudy diminishes when sphincter pupillae or round muscles agree and increments when dilator pupillae or spiral muscles contract. Then again, bars and cones are the photoreceptor cells present in the retina.

In this way, the right answer is 'Spiral and round muscles'.

Note:
The word iris is gotten from the Greek goddess of the rainbow, due to the numerous shades of the iris. The iris, the shaded aspect of the eye, fluctuates in shading from individual to individual. These shading contrasts are controlled by the measure of melanin present in the iris. Melanin is a sort of insoluble color present in a wide range of creature life.