THE WOLFFIAN BODIES. 609 



lung is seen to consist of a mass of csecal tubes issuing from 

 the branches of the trachea. (Fig. 243, c.) The diaphragm 

 is early developed. 



The Wolffian Bodies, Urinary Apparatus, and Sexual Organs. 



The Wolffian bodies are organs peculiar to the embryonic 

 state, and may be regarded as temporary, rather than rudi- 

 mental, kidneys; for although they seem to discharge the 

 functions of these latter organs, they are not developed into 

 them. They probably bear the same relation to the persistent 

 kidneys that the branchiae of Amphibia do to the lungs which 

 succeed them. 



In Mammalia, the Wolffian bodies (Fig. 244, W) are bean- 

 shaped, and are composed of transverse csecal canals, united 

 by an excretory duct (to), which leads from the lower extrem- 

 ity of the organ to the sinus urogenitalis of the foetus (Fig. 

 244, ug\ The kidneys (r) and suprarenal capsules (sr) are 

 developed behind them. Their size is at first so great that they 

 entirely conceal the kidneys ; but in proportion as the latter 

 bodies increase in size, they grow relatively smaller, and come 

 to be placed more inferiorly. At length, towards the end of 

 foetal life, only an atrophied remnant of them is left. Their 

 ducts, in the male, are ultimately developed to form the vas 

 deferens and ejaculatory duct of each side ; the vesiculse semi- 

 nales forming diverticula from their lower part. In the female, 

 the ducts of the Wolffian bodies disappear. 



The testicles or ovaries are formed independently at the 

 internal excavated border of these organs; and at first it is not 



Cible to say which of them the testicle or ovary the new 

 lation is to become. Gradually, however, the special char- 

 acters belonging to one of them are developed ; and in either 

 case the organ soon begins to assume a relatively lower posi- 

 tion in the body ; the ovaries being ultimately placed in the 

 pelvis ; while towards the end of foetal existence the testicles 

 descend into the scrotum, the testicle entering the internal 

 inguinal ring in the seventh month of foetal life, and complet- 

 ing its descent through the inguinal canal and external ring 

 into the scrotum by the end of the eighth month. A pouch of 

 peritoneum, the processus vaginalis, precedes it in its descent, 

 and ultimately forms the tunica vaginalis or serous covering 

 of the organ ; the communication between the tunica vaginalis 

 and the cavity of the peritoneum being closed only a short 

 time before birth. In its descent, the testicle or ovary of 

 course retains the bloodvessels, nerves, and lymphatics, which 

 were supplied to it while in the lumbar region, and which are 



