422 



THE EABBIT. 



cially at its hinder end ; but the more recent and very careful 

 observations of Martin show conclusively that it is merely a 

 case of very close apposition, and that the duct is really of 

 mesoblastic origin along its entire length : its mode of formation 

 being practically the same as that already described in the case 

 of the chick, p. 315. 



2. The Wolffian Body. 



The Wolffian body commences to form, in the latter part of 

 the ninth or early part of the tenth day, as a series of solid strings 



MS 



FIG. 164. A transverse section across the body of a Babbit Embryo of the 

 early part of the tenth day, showing the supposed epiblastic origin of 

 the Wolffian duct. (After Hensen.) x 75. 



A, dorsal aorta. AN", amuion. C, coalom, or body cavity. CH, notochord. H, 

 hypoblast. KC, Wolffian duct. ME, somatopleuric layer of mesoblast. MH, 

 splanchnopleuric layer of mesoblast. MS, mesoblastic somite or protovertebra. WS, 

 central canal of spinal cord. 



of cells, which lie to the inner side of the Wolffian duct along 

 almost its entire length. 



These strings of cells are stated to arise as ingrowths from 

 the peritoneal epithelium ; but the point is not definitely esta- 

 blished, and from a very early stage the strings lie embedded in 

 the mesoblast, and quite independent of the peritoneum. The 

 strings soon become tubular, and are then spoken of as the 

 Wolffian tubules. Each tubule opens at one end into the Wolffian 

 duct ; while its opposite, or blind end, becomes expanded into a 

 vesicle, and then doubled up on itself to form a Malpighian body> 

 into which a branch of the aorta quickly penetrates to form the 

 glomerulus (Fig. 165, GM). The Wolffian tubules are not seg- 



