Studying the kidneys of the Common Porpoise and the Fin Whale it was found that there is a second venal system next to the normal venal system. The arterial and venal system as found in the kidneys of the dog are present in the kidneys of the Common Porpoise without typical differences but there is also a venal system situated outside the renculi which conducts the blood from the venae arcutae to the vene cava. This system is found in the kidneys of the Common Seal but here it is replacing the system of the vena renalis which it does not do in the kidneys of the Common Porpoise. In the kidneys of the Common Porpoise and the Fin Whale both the plexus which surround the pelvic cavity and the ureter are present and they show to be nearly similar to those described for the kidneys of the dog. Between the renculi it is found that the plexus mentioned are somewhat more developed than in the dog. The morphology of the plexus is also identical to that of the plexus in the dog, and it is supposed that their function will be also the same in the Common Porpoise and in the dog.