62 



THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



AVASCULAR AREA OF FOLLICLE 



VASCULAR AREA OF FOLLICLE 



3,£/^ ^IMMATURE FOLLICLE 



"^ ' ~^ '' ' ^~" \RIAN 



CAVITY 



BLOOD 



SUPPLY 



HI LUS 



Fig. 32. Anterior half of the saccular ovary of Nectiirus maculosus. 



an opening into the urogenital sinus and thence to the outside as in 

 cyclostome fishes, 



(2) a short sinus-like tube attached to each ovary and to the urogenital 

 sinus or to a separate body opening as in many teleost fishes (fig. 

 28), and 



(3) two elongated oviducal tubes variously modified (figs. 29, 33, 34, 

 35, 36, 37). 



Except in the teleost fishes the cephalic end of each oviduct generally is 

 open and is placed near the ovary but not united directly with it (figs. 29, 

 33) although in some species, such as the rat, it is united with an ovarian 

 capsule (fig. 37). In some vertebrates the anterior orifice of the oviduct may 

 be located a considerable distance from the ovary, as in frogs, toads, and 

 salamanders. In many vertebrates, as in birds and snakes, there is but one 

 oviduct in the adult. 



In some vertebrates the oviduct is an elongated glandular tube, as in certain 

 urodele amphibia (fig. 33) and in ganoid fishes; in others, such as frogs, 

 birds or mammals, it is composed of two main parts: ( 1 ) an anterior glandular 

 structure and (2) a more caudally placed uterine portion. The latter may 

 unite directly with the cloaca, as in the frog (fig. 38) or by means of a third 

 portion, the vaginal canal or vagina located between the uterus and the 

 cloaca, as in elasmobranch fishes, reptiles, and birds, or between the uterus 

 and the external urogenital sinus, as in mammals (figs. 35, 36, 37). The 

 vaginal canal may be single, as in eutherian mammals, or double, as in meta- 

 therian mammals (figs. 35, 36). In metatherian (marsupial) mammals it 

 appears that a third connection with the oviducts is made by the addition 

 of a birth passageway. This birth canal represents a secondary modification 

 of a portion of the vaginal canals and associated structures (figs. 34, 35, 114). 

 (See Nelsen and Maxwell, '42.) One of the main functions of the vagina or 

 vaginal canal is to receive the intromittent organ of the male during copulation. 



