THE URINO-GENITAL SYSTEM 279 



dorsal aorta and the post-cardinal veins. A microscopic examination 

 of a series of transverse sections reveals its epithelial nature, and, 

 while a few nerve-cells may be present, it is definitely not a ganglion, 

 and their presence must be regarded as incidental and consequent 

 on its close proximity to a true ganglion of the sympathetic chain. 

 While, as already stated, the appearance of these bodies varies con- 

 siderably, they not infrequently consist of a hollow epithelial vesicle 

 with a knot of cells towards one side — in other words, they are 

 strongly reminiscent of an abortive Malpighian body. At other 

 times they are more dense and do not exhibit this appearance. Al- 

 though an investigation of their embryological history would be 

 necessary in order completely to elucidate their identity, it is sug- 

 gested that they are probably of nephric origin and may possibly 

 represent the vestige of a pronephros. 



Since there are definite sexual differences in the shape of the 

 kidneys as well as in the arrangement of the ureters it is necessary 

 to consider each sex separately. 



THE FEMALE SYSTEM (PI. XX) 

 I. The Kidneys and Ureters. 



The two sections of the kidney as outlined above are distinguish- 

 able, although the 'sexual kidney' is such in name only since it has 

 no connexion with the female gonad. It also merges more gradually 

 into the definitive kidney, which in turn is somewhat smaller in the 

 female than in the male. The ureters (utr.) or Wolffian ducts are very 

 different in the two sexes. In the female the duct of the 'sexual 

 kidney' is a very fine longitudinal canal lying close alongside 

 its lateral edge. This duct is joined at intervals by about eight 

 transverse tributaries from the tubules of the kidney. As it 

 approaches the 'definitive kidney' the Wolffian duct diverges some- 

 what from its edge and passes backwards via the mesentery 

 supporting the oviduct and, like this duct, becomes folded over to 

 the ventral side of the kidney just before entering the cloaca. It 

 receives tributaries from the kidney all the way along, and becomes 

 correspondingly thicker. The fact that these tributaries enter the 

 Wolffian duct approximately opposite the point where they leave 

 the kidney is in strong contrast to the condition in the male. The 

 duct opens into the cloaca at the apex of a small papilla just dorsal to 

 the opening of Miiller's duct (oviduct). It remains entirely separate 

 from Miiller's duct throughout its length, and does not discharge 

 into it as some of the early workers supposed. 



