DEVELOPMENT OF THE PIO DDEING FIRST TEN DAYS. 355 



vesicle depends, it would seem, directly upon the length of tlie 

 uterus, number of embryos, and the position of the embryos in 

 the uterus. 



The walls of the uterus are very soft, and the foldings of its 

 mucous membrane very complicated, and obliterate the lumen 

 of the tube almost completely. 



The several blastodermic vesicles do not overlap each other. 

 The highest up on each side is always longer than the others 

 in the same horn of the uterus. The longer ones are thinner 

 than the shorter ones. The vesicle is not folded back upon 

 itself, but crumpled like the sides of wind bellows. In one 

 sow killed upon the eighteenth day, the one which occupied 

 the highest position of one side, measured when removed 

 and unfolded forty-two inches. The length of the piece of 

 uterus which contained it was twelve inches. The two at 

 the lower ends of the horns of the uterus extend into the 

 vagina, and in one case were fused with each other, I 

 have never found any fusion between any of the vesicles 

 within the uterus, although their ends were in contact. 



References. 



1. AssHETON, R. — "A Re-investigation into the Early Stages of tlie 



Development of the Rabbit," 'Quart. Journ. Micr. Sci.,' vol. xxxvii, 

 1894. 

 la. AssHETON, R. — " The Segmentation of the Ovum of the Sheep, with 

 Observations on the Hypothesis of a Hypoblastic Origin for the 

 Trophoblast," 'Quart. Journ. Micr. Sci.,' vol. xli, 1898. 



2. VON Baer, K. E. — ' Ueber Entvi'ickehingsgeschichie der Tliiere,' 



Konigsberg, 1828. 



3. Balfotjk, F. M. — ' A Treatise on Comparative Embryology,' 2nd edit., 



London, 1885. 



4. Van Beneden, E. — ' De h. maturation d'oeuf, de la fecondation et des 



premiers pheiiomenes embryonaires chez les Mammiferes d'apres les 

 observations faites chez le lapin," ' Bulletin de I'Academie Royale des 

 Sciences de Belgique,' 1875. 



5. Van Beneden, E. — ' Recherches sur I'enibryologie des Mammiferes, 



La formation des feuillets chez le lapin," ' Archives de Biologic,' 

 tome i, 1880. 



