442 Bashford Dean Memorial Volume 



Mesonephric Ducts and Collecting Tubules. — In specimen No. IV, which is 

 immature, the mesonephric ducts are so slender that they are barely visible to the naked 

 eye, but with the aid of a dissecting lens they were easily recognizjed. They were identi' 

 fied also in transverse serial sections of the urogenital system taken at distances of ap' 

 proximately 25 mm., 140 mm. and 400 mm. from the posterior ends of the mesonephroi. 

 In all three regions the mesonephric ducts lie side by side — at 25 mm. and 140 mm., 

 close together within the dorsal mesentery; and at 400 mm., some little distance apart, 

 within the very narrow special mesenteries supporting the oviducts. The mesonephric 

 ducts are of equal si2,e. Collecting tubules were not positively identified. 



In specimen No. Ill the left mesonephric duct was probed for a distance of 25 mm. 

 from the left urinary sinus, and was bristled for an equal distance further. Throughout 

 this posterior 50 mm. of its course, it runs in the narrow dorsal mesentery. Due, perhaps, 

 to the poor preservation of the material, the duct could not be satisfactorily traced 

 further. No duct connected with the right urinary sinus could be found by dissection. 

 Collecting tubules could not be identified. A segment of the dorsal mesentery taken 

 about 100 mm. in front of the urethral pore was sectioned transversely. The sections 

 show two mesonephric ducts, side by side, but of unequal si2,e. The right duct is the 

 smaller, and in places is almost obliterated. 



Of my four specimens. No. I (Text-figures 87 and 93) is most favorable for the study 

 of the duct system. The left mesonephric duct (mes.d.) was easily probed, by way of the 

 left urinary sinus, for a distance of about 80 mm. in front of the urinary sinus. Through- 

 out this distance it runs in the dorsal mesentery; but just where the probe fails to 

 penetrate, the duct leaves the dorsal mesentery to enter the special mesentery supporting 

 the left uterus. In its further course the duct is quite conspicuous and it was easily 

 traced almost to the anterior end of the mesonephros. In the anterior third of the body 

 cavity, the duct again courses in the basal portion of the dorsal mesentery. The right 

 mesonephric duct has a similar distribution. It was probed for 80 mm. from the right 

 urinary sinus, but in general it is not quite so well developed as the left duct. Where 

 the two ducts course together in the dorsal mesentery they do not lie side by side. Poste- 

 riorly, the left duct is immediately dorsal to the right; anteriorly, the left duct is some 

 little distance ventral to the right. Collecting tubules (c.t.) entering the right duct are 

 about as numerous as those entering the left duct. All the tubules incline forward as 

 they course ventrad from the mesonephroi to the ducts. In the dorsal mesentery the 

 tubules leading to right and left ducts respectively are roughly alternate in position. 



Since the mesonephroi extend posteriorly much farther than the mesonephric ducts, 

 the question arises whether any collecting tubules from the posterior end of a mesonephros 

 enter the urinary sinus directly instead of by way of the mesonephric ducts. In the vicin- 

 ity of the urinary sinus the dorsal mesentery is rather thick and quite opaque, so that 

 it is difficult to determine whether collecting ducts are present. Nevertheless, two or 

 three collecting tubules were found entering the anterior end of each urinary sinus, as 

 shown for the right side in Text-figure 93. 



