THE OVIDUCTS 219 



Corjnis L/ifc/ni/ \'cnnii. (^'i,i,^ V-u .) 'I'liis hody is lii.stoloji;ic'ally 

 identical with the corjjiis lutcuin s])uriuiii (iurinfi; the first part of 

 its development. I lowever, if the ovum is fertilized and the embryo 

 im])lants, the corpus grows larger over a longer j^eriod of time than 

 the cori)Us Inteum spurium. Instead of reaching the climax and 

 beginning to degenerate shortly after ovulation it continues to 

 de\elop and remains present for the greater part of the period of 

 pregnancy. This structure begins to degenerate shortly before 

 birth of the embryo and with l)irth of the fetus it degenerates 

 rapidly to leave a corpus albicans. 



In mammals with relatively short cycles, such as the rat, numerous 

 ova are in the process of maturation and a number mature over 

 short intervals unless fertilization occurs. Numerous corpora are 

 formed in such forms and follicular changes are correspondingly 

 ra])id. 



THE OVIDUCTS. 



There are many variations in the egg-conducting apparatus. 

 In some forms, such as the cyclostomes, and some teleosts, no ovi- 

 ducts are present and the eggs liberated into the l)ody cavity pass 

 to the outside through ])ores in the cloacal region. In other teleosts, 

 folds of the ])eritoneum form funnel-like sacs connecting the ovary 

 with the cloaca. They are composed of fibroelastic connective 

 tissue with some smooth muscle and surfaced by a sim])le ei)ithelial 

 membrane. 



In some of the lower vertebrates it appears that the Wolffian 

 and Miillerian ducts arise from a longitudinal si)litting of the 

 embryonic j^ronephric duct. ^Ye have already observed that usu- 

 ally the oviducts or Miillerian ducts arise in both the male and 

 female as a fold in the ventral lateral siu'face of the mesonephric 

 cell mass near its anterior end. The anterior end forms a groo\'e 

 that remains open while posteriorly the fold forms a tube or corfl of 

 cells that develops a lumen. The j^osterior ])orti()n grows caudally 

 to fuse with the cloaca or urogenital sinus, but the anterior end 

 remains open into the body cavity and is called the ostium alxlomin- 

 alis. In elasmobranchs, am])hibians, birds, and monotremes, the 

 eggs pass into the abdominal ca\'ity and from there into the ostium 

 abdominalis of the oviduct to be conducted to the cloaca. 



In vertebrates below the manunals, as a rule, the two oviducts 

 open separately into the cloaca. In mammals, a longitudinal septa, 

 the perineum, divides the embryonic cloacal region into a dorsal 



