Can someone summarize The dual visual system to me AND color vision, like blindness etc...

Dual visual system:

Dual visual system is nothing but the different visual systems that our brain is meant to direct.

The two visual systems are

Dorsal Stream:

Dorsal stream is mainly referred as a vision of action. This visual system is involved in moment by moment analysis. It is also known as where stream.

Ventral Stream:

Ventral stream is mainly referred to as the vision of perception. This visual system is meant to analyse and recognize shape and object etc. It is also known as What stream

Blindness:

Blindness is a defined as the lack of vision. Such type of vision loss can't be corrected either by contact lens or through glasses.

There are two type of blindness,

Temporary blindness is a condition where the vision of an individual vision is limited.

Permanent Blindness is a condition where an individual can't see anything even the light

the answer is d.) homologous; have mammary glands

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.