54. 



OVUM. 



formative process of the ovum, including 

 the addition of the external coverings, is 

 completed within the ovary; and, on the 

 other hand, there are a few instances in 

 which, as in the trematoda and cestoid en- 

 tozoa, the germinal vesicle and yolk sub- 

 stance of the ovule are formed in separate 

 organs, instead of in the usual manner entirely 

 in the ovary. 



The varieties of the ovaries in different 

 animals may be considered under two heads 

 viz., 1st. Their relation to the passages or 

 outlets as influencing the mode of discharge 

 of the ova from them ; and 2nd, their internal 

 structure as related to the form of the ovum 

 produced. 



Fig. 36 



Ovary and oviduct of a laying Fowl, killed twelve 

 hours after laying the last egg. 



a. Left ovary ; b, opening of the infundibiilum of 

 the oviduct ; c, d, glandular portion of the oviduct ; 

 at d, the isthmus ; e, an egg in the uterine portion 

 of the oviduct, in which the shell is begun to be 

 deposited ; /, the rectum, ending in the cloaca ; g, 

 the undeveloped right oviduct occasionally met 

 with. 



a. Relations of the form of the ovaries to the 

 discharge of ova. In the majority of verte- 

 brated animals the ovary or ovaries are quite 

 detached from the conducting tube or ovi- 

 duct ; the ovules are formed in close capsules 

 of the ovary, by the bursting or fissure of the 

 wall of which they escape ; the oviduct opens 

 at its upper end into the abdominal cavity, 

 and there receives the ovum which has been 

 discharged from the ovary. This is the general 

 arrangement in mammalia, birds, reptiles, am- 

 phibia, and cartilaginous fishes. There is some 

 difference in the form of the ovary in the 

 higher and lower of these animals. In mam- 

 malia and birds, in chelonia and the crocodiles 

 among the reptiles, and in cartilaginous fishes 

 the ovary is more or less solid, and the ovules 

 are developed in capsules which project 

 towards the external surface ; but in the lizards 



Fig 37. 



(From Cams and Otto.) 



Female of the Falco buteo opened, showing the 

 left larger oviduct and ovary, and the smaller right 

 oviduct and ovary. a) a, the right and left ovaries ; 

 b, the left infiindibuhiin ; c, d, the left oviduct; ,/", 

 the rectum, ending in the cloaca, -which has been 

 opened, showing at /<' h the openings of the right 

 and left oviducts, and at i' i those of the ureters; g, 

 the vestige of the right oviduct. 



