Origin and Differentiation of Epithelium of Urinogenital Sinus in the Opossum

Abstract

Summary and Conclusions

1. Those epithelia in the urinogenital tract of the opossum which respond to estrogens by squamous metaplasia and cornification, have a common origin from the lining of the urinogenital sinus. 2. The sinus epithelium itself is apparently derived at an early stage of development from the ectodermal cloaca or uro-proctodeum, and perhaps in part from the urethral plate. 3. The primitive cloacal endoderm is eventually restricted to the bladder proper. 4. A common ectodermal origin best explains the histological and physiological likenesses of the tissues involved, and the occurrence of stratified squamous epithelium in the lower urinogenital tract of mammals generally. Early development in higher mammals needs reinvestigation with respect to this point. 5. The use of hormones (particularly estrogens) in the immature organism is a valuable method of precociously differentiating tissues not so readily delimited in normal development of the urinogenital tract.