A comparison of certain features of the testis and epididymis has been made in five species of East African mammals, two of which, the rock hyrax and elephant, have abdominally situated testes.
The artery to the testes was straight in the species with abdominally situated testes and there was no pampiniform plexus while in the species with scrotal testes, it was coiled in the region of the plexus. It is suggested that where the testicular artery is coiled, the testes should be regarded as basically scrotal, even if they are usually found in the abdomen post mortem.
A striking increase in blood flow in the testis of the rock hyrax during sexual activity suggests that the simpler arterial pattern of the testis in testicond mammals allows a greater variation in blood flow than the more complicated arterial design associated with scrotal testes.
Characteristic signs of sperm maturation occur in the epididymis of testicond mammals in contrast to the situation in artificial cryptorchidism, where normal epididymal function is completely disrupted. It is suggested that epididymal function, as well as spermatogenesis, has become modified during evolution. Evidence is given that a need for prolonged survival of spermatozoa in the mesonephric duct might have been an important primary factor in the caudal migration of gonads into a scrotum.