This feature is consistent with the tegument appearance of other terminally spined schistosomes. An ELISA test can be performed to test for antibodies specific to schistosomes. The eggs of all trematodes (except schistosomes) are operculated. Most of the body mass of female schistosomes is devoted to the reproductive system. Brant and Loker used endothermy as a key factor in the diversification of schistosomes. The life cycle of "T. regenti" is analogous to that of human schistosomes. This has been observed in the population dynamics of "Schistosomes". Its fruits contain diosgenin, a hormone precursor that presumably hinders the development of schistosomes. Infection by schistosomes is followed by an acute Katayama fever. The blood flukes, such as schistosomes, spirorchiids and sanguinicolids, feed exclusively on blood. The species that infect humans can be divided into groups, the schistosomes and the non-schistosomes. Other parasitic worms such as schistosomes reside in blood vessels. Schistosomes, which cause the devastating tropical disease bilharzia, belong to this group. The four species of schistosomes that infect humans are members of the genus "Schistosoma". Adult schistosomes share all the fundamental features of the digenea.