422 A Three Weeks' Human Embryo 



protruding part of the ridge. At the other extremity of the tubule it 

 joins the Wolffian duct. 



In a eat from which a part of the mesonephros was modeled, the next 

 stage apparently was found. Some of the centrally located sub-cylindrical 

 tubules open from the coelom at the crest of the Wolffian ridge, and at the 

 other end of the tubule into the Wolffian duct. The general appearance 

 of these tubules and their connections is perfectly comparable to the con- 

 dition found in the early shark, the tubules of which were also modeled 

 and found to differ from those of the cat in the fact that they were more 

 S-shaped. 



No. 1-18 (Figs. 17-20) furnishes the next stage. It has apparently 

 in its series of twenty or more tubules a complete recapitulation of the 

 preceding stages co-existing with the commDnly recognized type-form 

 of tubule. 



There are : — 1st, The Wolffian duct in the caudal part, having no con- 

 nection with the tubules, but presenting a series of distinct enlargements ; 

 2d, Aggregations of cells with no apparent lumen, and no connection 

 with the ccelomic epithelium or the duct; 3d, Cavities or vesicles deep in 

 the Wolffian ridge surrounded by a several-layered epithelium, and having 

 no connection with either ccelomic epithelium or duct; 4th, Similar 

 vesicles lying near to the ccelomic epithelium of the crest of the Wolffian 

 body, connected with that epithelium by (a) a solid string, (b) a narrow 

 open channel, or (c) a wide open funnel (Fig. 20) ; 5th, In the cephalic 

 half, one tubule, the 7th, with a slight opening from the Bowman's 

 capsule to the ccelomic epithelium; 6th, The remainder (8th, 6th, 5th, 

 4th, 3d) of the cephalic group have the typical Bowman's capsule, the 

 S-shaped tube, and the connection with the Wolffian duct but no connec- 

 tion with the coelom (Fig. 19) ; 7th, The 2d tubule having two Bowman's 

 capsules, one dorsad of the other, that is, an apparent beginning of the 

 dorso-ventral division of the tubules; 8th, The 1st small tubule, appar- 

 ently consisting only of a Bowman's capsule, sessile on the beginning of 

 the Wolffian duct. 



The arterv and vein supplying the rudimentary glomerulus of these 

 Bowman's capsules (Fig. 6) could in a few places be clearly seen. The 

 specimen not being favorable to the study of blood-vessels, the vascular 

 supply could not always be made out. 



Such a tubule as was found in the cat with both ends open (see above) 

 did not occur in Xo. 148. The tubules which had attained connection 

 with the duct had in this specimen apparently lost connection with the 

 ccelomic epithelium. In No. 80 (MacCallum") the transitional forms 



