Mammals evolved during the Triassic period. I believe the first mammal was like a tiny shrew-like animals. They called it the Eutherian. But the actually mammals were the dinosaurs.
The structure which is separate from the apoplastic route is THE LUMEN OF SIEVE TUBE.
Apoplastic route is found in plants where they facilitate the transport of water and solutes accross a tissue or organ. In the plant cells, apoplast is the space at the outside of the plasma membrane within which material can diffuse freely. The apoplastic pathway allows water to move from cell wall to cell wall without entering the cell cytoplasm.
I want to say that the answer is A
The correct answer is an increased number of rod cells.
In eyes of the humans, and many other animals there are two types of receptors, the rods, and the cones. The cones have an important role in color vision and they possess different types of pigment which enable color vision.
On the other hand, the rods are more sensitive to light, and they are responsible for black and white vision.
Therefore, an increase in the number of rods can enable the animal to see betther in the dark.