G52 ox THE UEOGENITAL ORGANS OF THE KANGAEOO, 



of the cul-de-sac much wider from side to side than the former, 

 and about the same height from above downwards ; and lastly 

 below and on either side of the middle aperture, come the open- 

 ings of the lateral canals w^hich at first are quite separate from 

 one another and merely connected loosely by connective tissue, 

 but in the very last part of their course their inner walls fuse 

 and so in sections they are separated by a narrow septum. The 

 outline of the openings is more or less convoluted. The follow- 

 ing changes then take place in successive sections of three of the 

 specimens. The urethral aperture gradually becomes smaller 

 and finally opens into the urogenital passage, its ostium being 

 situated on the median ridge. The aperture of the cul-de-sac 

 after having gradually diminished in size until it is no bigger 

 than a pinhole, disappears altogether. This happened in the 

 23rd, 17th, and IGth sections respectively, before the septum 

 between the apertures of the lateral canals thins away, until they 

 are no longer separated, and now give rise to the anterior portion 

 of the urogenital canal. The sections intervening between the 

 last shewing the aperture of the cul-de-sac and the first shewing 

 the meatus urinarius were carefully counted, and were found to 

 be 45, 50, and 11 respectively, (equal to about i in.). 



The fourth specimen presented some interesting differences. 

 In the earlier sections which were ~i\ in. from side to side, the 

 aperture of the cul-de-sac measured f in. in the same direction, 

 and averaged -} in. from above downwards, but was slightly wider 

 than this just at one end. Then, instead of diminishing to a pin- 

 hole as before, it became blocked for l- in. in the middle only. 

 The blocking increases in width from side to side in succeeding 

 sections, until in the course of half a dozen of them, there is 

 nothing left of the original aperture but a small hole at either 

 extremity, the intervening space having been completely filled up. 



Next in the course of a few sections, one of these holes 

 disappears entirely, while the other continues much as before. 

 Between fifty and sixty consecutive sections had been mounted 



