DEVELOPMENT. WOLFFIAN BODIES. 



993 



Wolffian Bodies. In the embryos of the higher mammalia these organs are propor- 

 tionally smaller, and disappear earlier than in those of the lower mammalia, birds, 

 or reptiles. In' the human subject, accordingly, the Wolffian bodies are relatively 

 small, and are found only in an early stage of foetal development. In the mammalian 

 embryo, at a period when the intestinal canal still communicates with the umbilical 

 vesicle by a wide orifice, the Wolffian bodies appear in the form of two slight ridges 

 of blastema, placed one on each side of the line of attachment of the intestine to the 

 vertebral column. On reaching their full size, which in man seems to take place 

 about the fifth week of embryonic life, they have the appearance of two oblong 

 reddish masses placed on the aides of the vertebral column, and extending from the 

 lower end of the abdomen to the vicinity of the heart. Their structure is glandular ; 

 clear pedunculated vesicles may be early discovered in them, opening into an excretory 



Fig. 691. DIAGRAM OP THE Fig. 691. 



WOLFFIAN BODIES, MULLERIAN 

 DUCTS, AND ADJACENT PARTS, 

 PREVIOUS TO SKXITAL DISTINC- 

 TION, AS SEEN FROM BEFORE. 



s r, the suprarenal bodies ; r, 

 kidneys; ot, common blastema of 

 ovaries or testicles ; W, Wolffian 

 bodies ; w, Wolffian ducts ; m, m, 

 Miillerian ducts ; yc, genital cord ; 

 u g, sinus urogenitalis ; i, intes- 

 tine ; c I, cloaca. 



duct which runs along the outer 

 side of each organ. These 

 vesicles subsequently become 

 lengthened into transverse and 

 somewhat tortuous ccecal tubes, 

 which still retain a dilatation, 

 like the capsule of a Malpighian 

 body, at their inner extremity. 

 The Wolffian bodies are highly 

 vascular, their larger blood- 

 vessels running between and 

 parallel with the transverse 

 tubules. In the embryo of the 

 coluber natrix, Rathke first 

 observed vascular tufts, which 

 he compared to the Malpighian 

 corpuscles of the kidneys; and 

 since the time of his discovery, 



Malpighian tufts have been found in the Wolffian bodies of birds and mammals. 

 The ducts of the two bodies open into the sac of the allantois, to be presently 

 described. 



A whitish secretion has been seen in the ducts of the Wolffian bodies of birds and 

 serpents resembling the urine of those animals, and as the fluid of the allantois also 

 has been found to contain uric acid, it is reasonable to think that the Wolffian bodies 

 perform the office of kidneys during the early part of foetal life. They are accord- 

 ingly sometimes named the primitive or primordial kidneys. 



As development advances, the Wolffian bodies rapidly become proportionally 

 shorter and thicker : they shrink towards the lower part of the abdominal cavity, and 

 soon become almost entirely wasted. By the middle of the third month only traces of 

 them are visible in the human embryo. They take no part in the formation of the 

 kidneys or suprarenal capsules, nor in that of the ovaries or body of the testes, but 

 are connected with the origin of a part of the seminal passages in the male sex. 



The Kidneys and Ureters. The kidneys commence subsequently to and independ- 

 ently of the Wolffian bodies. They already exist about the seventh week, as two small 



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