272 WOLFFIAN BODY AND KIDNEY. 



anterior segments as a distinct gland, wbicli was spoken of in 

 the description of tlie adult as the kidney proper, while the 

 unaltered preceding segments of the kidney were spoken of 

 as the Wolffian body. 



It will be remembered that each segment of the embryonic 

 kidney consists of four divisions, the last or fourth of which 

 opens into the Wolffian duct. The changes which take place 

 in the hindermost ten or eleven segments, and cause them 

 to become distinguished as the kidney proper, concern alone 

 the fourth division of each segment, which becomes prolonged 

 backwards, and its opening into the Wolffian duct proportion- 

 ately shifted. These changes affect the foremost segments of 

 the kidney much more than the hiudermost, so that the fourth 

 division in the foremost segments becomes very much longer 

 than in the hindermost, and at last all the prolongations of the 

 kidney segments come to open nearly on the same level, close 

 to the cloacal termination of the Wolffian duct (PL XX. fig. 8). 

 The prolongations of the fourth division of the kidney-seg- 

 ments have already (p. 251) been spoken of in the description 

 of the adult as ureters, and this name will be employed for 

 them in the present section. 



The exact manner in which the changes, that have been 

 briefly related, take place is rather curious, and very difficult 

 to unravel without the aid of longitudinal sections. First of 

 all, the junction between each segment of the kidoey and the 

 Wolffian duct becomes so elongated as to occupy the whole 

 interval between the junctions of the two neighbouring seg- 

 ments. The original opening of each tube into the Wolffian 

 duct is situated at the anterior end of this elongated attach- 

 ment, the remaining part of the attachment being formed solely 

 of a ridge of cells on the dorsal side of the Wolffian duct. The 

 general character of this growth will be understood by com- 

 paring fig. 7 a and 7 h, PI. xx. — two longitudinal vertical sec- 

 tions through part of the kidneys. Fig. 7 a shews the normal 

 junction of a segmental tube with the Wolffian duct in the 

 Wolffian body, while in figure 7 h (r. u) is shewn the modified 

 junction in the region of the kidney proper in the same em- 

 bryo. The latter of these figures (fig. 7 h) appears to me to 

 prove that the elongation of the attachments between the 



