336 HISTORY OF THE HUMAN BODY 



male the testes are accompanied by an epididymis and a ductus 

 deferens, respectively the anterior portion of the mesonephros 

 and the mesonephrotic duct; and in the female there is an 

 oviduct with an enlarged ostium, into which the wandering 

 ova are received. In the present treatise the details of these 

 parts in reptiles and birds cannot be considered further, but the 

 history that is shown in mammals is of much importance, as 

 it includes the human conditions. 



In the mammalian embryo the mesonephrotic system at- 

 tains a high degree of development, and the mesonephros, 

 under the name of the " Wolffian body," is large and con- 

 spicuous. In the marsupial young of monotremes and mar- 

 supials it forms the functional kidney, and as this is but one 

 of several organs that become profoundly modified or replaced 

 during later life, the development may be rightly considered a 

 true metamorphosis in which the marsupial young represent a 

 larval stage. In placental mammals a similar replacement of 

 urinary systems takes place, but as the intra-uterine life is here 

 made longer than in former cases and includes also approxi- 

 mately the period passed by lower mammals in the marsupial 

 pouch, there is no free larva, and the changes are considered 

 a part of the embryonic development. 



As both the stage of the functional mesonephros and its 

 later reduction are of importance in understanding the adult 

 conditions, they may be first studied by the aid of the accom- 

 panying Plate. During the period designated as that of sexual 

 indifference, which includes all the early development and 

 continues until the embryo is quite well matured in many 

 other particulars (up to 70 or 80 days in the human species), 

 the sexes, although definitely determined, show absolutely no 

 difference in the general appearance of the uro-genital organs. 

 [Plate III, a]. The mesonephros is large and functional and 

 stands out freely from the dorsal wall of the abdomen, held 

 in place by a suspensory fold of peritoneum, the mesonephrotic 

 ligament. This fold becomes prolonged posteriorly beyond 

 the limits of the Wolffian body and forms the inguinal liga- 

 ment, a part of great importance in subsequent relationships. 



