BY JAS. P. HILL AND C. J. MARTIN. 63 



while a short distance further forward a single distinct lumen 

 occurs, but it is confined to one section. Apparently we have 

 here to do with the last traces of the notochordal canal. 



The head process diminishes in thickness anteriorly and finally 

 passes into the posterior end of the notochord. 



WoIffia7i duct and body : The appearance of the Anlagen of the 

 Wolffian duct and body has already been described in surface 

 view\ In sections of its anterior region from the 4th to the 7th 

 somites the united Anlagen of the Wolffian duct and body appear 

 as a solid cord of cells projecting from the intermediate cell mass. 

 The greater part of the cord lies free betw^een the outer edges of 

 the somites and the lateral mesoderm, while its dorsal surface 

 approaches within a short distance of the ectoderm (fig. 8, w. h.). 

 As the cord is traced backwards it is found to become gradually 

 constricted in its middle region, while its dorsal portion broadens 

 out, until it becomes somewhat dumb-bell-shaped in form. Its 

 basal portion is now very distinctly connected with the lateral 

 mesoderm on its outer side. On its inner side, how^ever, the 

 connection with the somites is not now so well marked, and in 

 places this connection is completely lost. At about the level of 

 the 6th somite the constriction of the middle region of the cord 

 is much more marked, and it here consists of a ventral larger 

 rounded mass connected by a narrow isthmus with a dorsal much 

 thinner flattened band. The upper portion is the Anlage of the 

 Wolffian duct, while the lower is the Anlage of the Wolffian 

 tubules. Then, by the gradual disappearance of the connecting- 

 isthmus the mass comes to consist of a dorsal band-like Wolffian 

 duct Anlage (tig. 25, to.a.)^ united at its mid-region to the under- 

 lying Anlage of the tubules [tv.t.). Finally, opposite the 7th 

 somite the narrow connection betweeii the duct Anlage and the 

 Anlage of the tubules is lost altogether, and the two become 

 separate (fig. 26). 



The outer edges of the duct Anlage lie close l)elow the ectoderm 

 which, just over the duct, is very thin and delicate, and with very 

 few nuclei as compared with the rest of the ectoderm. Very 



