Our previous paper (1) predicted that there would be phenomena of decreasing volume concentrations of two-phase fluid containing solid spherical particles with the same specific gravity as fluid phase by flowing out through branch pipes. So the fluid was let flow through a circular pipe, and was partially let flow out through a branch circular pipe to study ratios of volume concentrations of fluid flowing out through branch pipes and those in a main pipe before branches. As a result, volume concentration ratios decreased as products of velocity ratios and diameter ratios increased. Volume concentrations in branch pipes were calculated by using potential flow models under the assumption that the fluid flowing in the layer between the wall and the plane apart a particle radius from the wall had no volume concentration of particle phase. The calculated results were found to agree with the experimental results fairly well as the prediction of our previous paper. One of the reasons why red blood corpuscles of mammals evolved into a flexible doughnut shape was considered. The shape would reduce the effects of these phenomena, and it would increase the number of blood corpuscles in capillaries. It would make it possible to use more delicate capillary systems and to evolve into higher organisms.