118 



THE WOLFFIAN DUCT AND BODY. 



of the body, where it becomes detached from the epiblast, and is connected with and 

 opens into the hind-gut (cloaca). 



I have here followed what has appeared to me the most probable account of the origin of 

 the duct (Martin, Strahl), but it is right to state that in the opinion of some observers 

 (Hensen. Spee, Flemming) the formation and growth of the duct in connection with the 

 epiblast is primary, especially in mammals, and the duct is originally formed by a longitudinal 

 thickening and involution of the epiblast, which only secondarily becomes connected with the 

 intermediate cell-mass. Compare also Haddon, Origin of segmental duct, Proc. Roy. Dublin 

 Society, Vol. V. 



In teleosteans (Rosenburg) and amphibia (Gotte) the Wolffian duct has been described as 

 developing in the form of a longitudinal groove-like invagination of the somatopleural meso- 

 blast (Balfour, Comp. Emb., vol. ii., pp. 580, 582), but more recent researches appear to indi- 

 cate that in these animals also the epiblast may be concerned in its formation. 



The Wolffian body developes in the intermediate cell-mass between the Wolffian 

 duct and the body-cavity as a series of transverse tubes which lie at right angles to 

 the course of the Wolffian duct, and open into it at regular intervals. The usual 



Fig. 140. TRANSVERSE SEC- 

 TION OP THE TRUNK OF A 

 CAT EMBRYO, SHOWING THE 

 VESICULAR STAGE OF THE 

 WOLFFIAN TUBULES. 



(E. A. S.) 



m.p., muscle plate ; ao, 

 aorta ; m.g., mid-gut ; am, 

 amnion ; iv, vesicle of Wolffian 

 body ; w.d., Wolffian duct ; 

 cce, ccelom. 



mode of formation of 

 these tubes which are 

 sometimes termed seg- 

 mental tubes appears 

 to consist in the accu- 

 mulation at regular intervals, corresponding with the somites, of rounded masses 

 of mesoblast on the mesial or ventral side of the Wolffian duct (fig. 142, w.l.), 

 which masses become afterwards hollowed out so as to form small vesicles, at 

 first isolated, but afterwards growing towards and opening into the Wolffian 

 duct (fig. 140). 1 Corresponding with these vesicles there become formed invagi- 

 nations of the epithelium of the body-cavity (fig. 141, st), which is thickened 

 along the inner side of the Wolffian projection, and grows at regular intervals 

 towards the vesicles. These ingrowths may at first communicate by funnel-shaped 

 openings, which in some lower vertebrates are lined by ciliated epithelium, with 

 the body-cavity, but the openings in higher vertebrates become closed again before 

 communication with the Wolffian duct is established. Finally, the connection 

 between the Wolffian tubes and the peritoneal epithelium is completely severed, and 

 the condition of simple or curved transverse tubes, blind at their inner ends and 

 opening at their outer ends into the Wolffian duct, is produced (fig. 142, B). After 

 a time the blind extremities are seen to be enlarged and spoon-shaped, and glomeruli 



1 According to v. Wijhe the hollow condition is the primary one in elasmobranchs, and the cavity of 

 each vesicle represents an intermediate part of the ccelcm of the segment (meso-coelom), the dorsal 

 ccelom being represented by the cavity of the proto-vercebra and the ventral ccelom by the pleuroperi- 

 toneal space. I have myself observed this condition of a hollow intermediate cell-mass communicating 

 on the one hand with the cavity of the protovertebra and on the other with the cleft of the lateral 

 mesoblast, in a chick of 36 hours (see fig. 139). 



In mammals the Wolffian vesicles are more numerous than the segments. 



