334 DR D- BERRY HART. 



the primitive gut. The term ' entodermal cloaca ' is apt to be 

 confused with the term cloaca, used legitimately enough at a 

 later stage of development for the common inferior aperture 

 in the six weeks' embryo or in the permanent organs of the 

 ornithorhynchus. I beg to suggest that we might speak of the 

 ' end-gut ' as the pars ultima ; of the ' entodermal cloaca ' as the 

 2Mrs penultima ; of the ' cloacal membrane ' as the anterior gut 

 membrane, short for anterior penultimate gut membrane. 



Into the so-called entodermal cloaca the Wolffian ducts open. 

 These have their origin from the ectoderm, as has been shown 

 for the guinea-pig by Graf Spee, and by Kollmann for the 

 human embryo. 



In an eight millimetre foetus (sagittal mesial section) further 

 changes are shown by Keibel. The end-gut (pars ultima) 

 (fig. 5) is in course of disappearance, while from the lower end 

 of the Wolffian duct the ureter is taking its origin. The penul- 

 timate gut (entodermal cloaca) now becomes divided by coronal 

 (side lateral) folds into an anterior and posterior part, the 

 closure proceeding from above down ; the posterior division 

 forms the rectum ultimately ; the anterior, part of the bladder 

 and the urinogenital sinus (figs. 6-9). In the guinea-pig a 

 peritoneal dip separates the upper parts of these organs 

 (Keibel). 



In the guinea-pig, where the allantois is very transitory, and 

 at any rate where no entodermal allantois is present at the time 

 the bladder develops, the urinary viscus arises, according to 

 Keibel, from the anterior division of the penultimate gut. In 

 the human embryo the stalk of the allantois is usually described 

 as giving origin to the bladder, but we must remember that in 

 the human embryo the allantois is quite rudimentary, and that 

 it seems more exact to describe the bladder as also originating 

 in the human embryo from the front division of the penulti- 

 mate gut (entodermal cloaca), with probably only its upper part 

 allantoic. The folds so dividing off the primitive gut are 

 coronal, as Keibel's sections show. He also points out that 

 the epithelial lining of the two divisions so formed is different, 

 prior to division, that of the future rectum being more 

 columnar (figs. 6 and 7). 



This view of the origin of the bladder, which we owe to 



