WOLFFIAN DUCT AND BODY IN THE CHICK. i5 



the WolfBan tubules and their connection with the Wolffian 

 duct is deferred behind the 15th segment. 



To sum up the developmental changes above recorded,, the 

 Wolffian duct arises as a continuous ridge of cells projecting 

 from the intermediate cell mass towards the epiblast in the 

 region of the 7th to 11th proto vertebrae inclusive. This ridge 

 separates from the intermediate cell mass from before backwards, 

 remaining, however, connected with it at intervals bj the rudi- 

 mentary Wolffian tubules. Meanwhile, from the hind end of it 

 there grows back a cord of cells independent at first of the 

 adjacent structures, but immediately on the formation of the 

 hinder segments becoming connected with the intermediate 

 cell mass of each segment in turn. This happens as far back 

 as the 15th segment; behind this point it grows back as a 

 solid cord, wliich does not become connected with the inter- 

 mediate cell mass until the tubules of the Wolffian body have 

 made considerable advance in their development. 



Pigs. 1 — 7 are meant to illustrate the above method of develop- 

 ment. Figs. 1 — 5 are from the 10th segment of chicks, with 

 ten, twelve, thirteen, and fourteen protovertebrae respectively. 

 They are all taken through points where the Wolffian duct remains 

 attached to the peritoneal epithelium, i.e. through a rudimentary 

 tubule, excepting fig. 4, which is from a section close to fig. 3, 

 and shows the condition of things in one of the intervals between 

 the points of continuity. 



Fig. 6 is taken from a section just behind the last segment of 

 a chick with twelve segments, and shows the complete inde- 

 pendence of the Wolffian duct. 



Fig. 7 is from the 13th segment of a chick with thirteen seg- 

 ments, i.e. from the same region as fig. 6, and it shows the con- 

 nection which has become established between the Wolffian 

 duct and the intermediate cell mass by a mutual growth of these 

 structures. 



Fig. 8 is from the 16th segment of a chick with twenty-two 

 protovertebrse, and is illustrative of the fact derived from an 

 inspection of all the sections of the segment, that the Wolffian 

 duct is independent of the peritoneal epithelium. From the 

 15th segment the Wolffian duct grows back independently to 

 the cloaca, into which it eventually opens, and a lumen appears 

 in it from before backwards. 



In fig. 11, taken from a chick at the end, of the third day, it 

 is still distinct from the now considerably developed Wolffian 

 tubule (w.t.). 



For purposes of description I shall divide the Wolffian body 

 into three regions — (1) The part found within the limits of the 

 7th — 11th segments inclusive; (3) the part found withm the 



