332 DR D. BERRY HART. 



several disappointments in this way. It is a safe plan, there- 

 fore, not to cut and stain all the serial sections unless the early 

 ones show the tissues to promise well. 



(b) The genital tract in the adult rabbit, and especially in the 

 rat-kangaroo, two specimens : Bennett's kangaroo, one specimen ; 

 Wallaby kangaroo, one specimen ; pelvis of Bennett's kangaroo, 

 one specimen from Professor Symington of Belfast ; many speci- 

 mens of early pig and rabbit embryo were also cut in serial 

 sections, as well as adult specimens of mole. 



The specimens were thus numerous, several thousands of 

 microscopical slides requiring careful examination. 



I also examined a series of early chick embryos prepared by 

 Mr Eichard j\Iuir. 



In determining the scope of this examination, I was guided by 

 the following criteria. In endeavouring to settle morphological 

 questions as already defined one should know — 



1. The development of the urinogenital organs in the 



embryo. 



2. The structure of these organs as modified in the female 



adult. 



3. The structure of these organs as modified in the male 



adult. 



These criteria I can fulfil with a fair amount of detail in the 

 human foetus and adult. In the other groups of mammals the 

 work is necessarily only partial. 



I. The Development of the Urinogenital Organs, Eectum 

 AND External Genitals in the Human Foetus up to the 



END OF THE FIRST MoNTH. ThE DEVELOPMENT OF THE 



Permanent Kidney is not considered. 



The development of the urinogenital organs is intimately 

 bound up with the origin of, and further changes in, the 

 primitive gut. 



If we examine the sections of the caudal end of a four milli- 

 metre human embryo as figured by Keibel (fig. 1), we see the 

 parts of the primitive gut known as the end-gut and the ento- 

 dermal cloaca. Anteriorly the latter is l)Ounded by what is 



