A renal portal system is a second route by which blood pools from a capillary bed into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are considered part of the renal portal system. The renal portal system is found only in fishes, amphibians (frog), reptiles and birds. Mammals ( rabbit, mouse and horse) have no renal portal system. So, the correct answer is option d.

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