1936 



HUMAN ANATOMY. 



Aorta 



Wolffian 



esothelit 



Wolffian tubule 



Aortic 

 branch to 

 glomerulus 



Developing capsule 



Part of transverse section of embryo, showing commencing develop- 

 ment of Malpighian corpuscle in WolfBan body. X 150. 



rudimentary character of- the pronephros, the Wolffian body not only serves for a time as the 

 chief excretory organ of the embryo, but in many lower vertebrates continues to functionate 

 during- life. The aniage of the Wolffian duct first appears as bud- like outgrowths from the dor- 

 sal side of the intermediate cell-mass ; these fuse into a strand which, separating from the cell- 

 mass, lies as a solid cord beneath 

 Fig. 1640. the ectoblast. The latter takes no 



Ao, part in the formation of the duct, 



'^e^ which is entirely of mesoblastic 



origin, the appearances leading to 

 the assumption by certain authori- 

 ties of its deri\ation from the outer 

 germ-layer depending upon the 

 temporary apposition or attach- 

 ment that the duct effects in con- 

 sequence, probably, of its inher- 

 ited inclination, since in ancestral 

 forms the tubules opened on the 

 free ectoblastic surface. At first 

 solid, the Wolffian duct later pos- 

 sesses a lumen which gradually 

 follows the tailward growth of the 

 strand until, finally, it opens into 

 the dilated end-gut or cloaca. 



In mammals the Wolffian 

 tubules are developed within the 

 ventral division of the intermedi- 

 ate cell-mass as solid cords that 

 later acquire a luinen and an at- 

 tachment to the Wolffian duct. Although in the lower vertebrates (fishes, amphibians) retain- 

 ing a communication with the coelom by means of a nephrostome, in mammals this connection 

 is lost and the expanded inner end of each tubule comes in close relation uith the convoluted 

 vascular tuft, the glomerulus, which now, however, no longer projects freely into the body- 

 cavity. As in the kidney, the glomerulus is supplied by an afferent twig from a branch of the 

 aorta, and is drained by an efferent vessel that breaks up into a capillary net-work surrounding 

 the convoluted tubule and eventually 

 becomes tributary to the cardinal vein. Fig. 1641. 



The first appearance of the Wolffian 

 body in the human embryo occurs very 

 early (2.4 mm. length) and at a time 

 when the remains of the pronephros are 

 still present. The duct precedes the 

 tubules and opens into the cloaca in em- 

 bryos of 4.2 mm. length (Keibel), the 

 tubules, which develop independently, 

 establishing communication with the 

 duct shortly before. The development 

 of the glomeruli is relatively tardy, since 

 these bodies are not found until the 

 human embryo has attained a length 

 of about 7 mm. Their formation and 

 growth continue during the first and 

 second months until the embryo meas- 

 ures 22 mm. in length, when their great- 

 est perfection is reached (Nagel). 



When fully developed, about the 

 end of the second month, the Wolffian 

 body appears as an elongated organ 

 ( Fig. 1720") which extends along almost 

 the entire length of the posterior wall 

 of the body-cavity, on either side of the 

 mid-line, from behind the lung-anlage to 

 the lower end of the gut-tube. About 

 the eighth week, the Wolffian body en- 

 ters upon its stage of regression which, 

 continuing dunng the third and fourth 

 months of foetal life, results in the grad- 

 ual atrophy of the organ and its replace- 

 ment as the functionating excretory 

 gland by the kidney which meanwhile 

 has been formed. This atrophy involves 

 first the glomeruli of the anterior portion of the organ, which, together with many of the tubules, 

 completely degenerate, the retrogressive process extending tailward and gradually involving the 

 middle and posterior segments. " Although the glomeruli suffer destruction, some of the tubules 

 and the Wolffian duct for a time remain and contribute in varying degree, according to the sex 



Capsule of 

 body 



Indifferent 

 sexual 

 gland 



Malpighian 



Wolffian 

 tubules 



Glomerulus 



Body-cavity 



Wolffian duct 



Transverse section of fully developed Wolffian body, 

 showing also indifferent sexual gland. X 80. 



