426 JAS. P. HILL. 



my owu dissections of nou-gravid geuital organs I had dis- 

 covered no such median passage. I was therefore considerably 

 surprised to fiud the allantoic stalk extendiug straight back 

 iuto the connective tissue between the lateral vagiual canals, 

 and not into one of the latter, which I had believed must 

 serve for the passage of the young at birth in spite of the 

 narrowness of their communications with the uterine cavities. 

 The novel features revealed in the dissection were, however, 

 further elucidated by series of transverse sections across the 

 urino-genital strand^ (fig. 25, w. s.), which demonstrated the 

 existence of a slit-like passage enclosing the allantoic stalks, 

 one from each uterus. 



On investigation the stalks could be traced down the median 

 pseudo-vaginal passage from the centre of the inner wall of 

 the allantois for a distance of about 3 cm. They did not 

 extend quite to the extreme posterior end of the urino-genital 

 strand shown in fig. 25, but this is no doubt to be accounted 

 for by tearing of the stalks in the process of removal of the 

 genital organs. In part of their course they were found to be 

 looped upon themselves. 



In Stage D the allantoic stalk of the larger embryo mea- 

 sured only about 8 mm. in length, so that shortly prior to or 

 during parturition a very considerable lengthening of the 

 stalks must take place. The stalk no doubt becomes severed 

 from the embryo only at the moment of birth, leaving merely 

 an insignificant portion (in length about "5 mm.) attached at 

 the navel of the latter (fig. 36). Similarly, in Brinaceus, 

 Hubrecht (9, p. 347) has shown that '^by far the longer 

 portion " of the strand formed by the lengthened- out allantoic 

 vessels at parturition remains attached to the afterbirth, which, 

 though eventually shed, is found in the uterus shortly after 

 delivery. 



A section of the mid region of the urino-genital strand of 



• This name is applied to the elongated mass of connective tissue in which 

 are embedded the lateral vaginal canals and urethra. It is united to its sur- 

 roundings by more areolar connective tissue, and is of very considerable 

 length. 



