EGG AND FEMALE ORGANS OF GENERATION. 687 



Ovaries and Oviducts. The eggs are produced in the interior of 

 certain organs, situated in the abdominal cavity, called the ovaries. 

 These organs consist of a mass of vascular connective tissue, inclosing 

 a number of globular sacs or follicles, the " Graafian follicles ;" so 

 called from the name of the anatomist who first fully described them 1 

 as constituent parts of the ovary. Each Graafian follicle contains an 

 egg, which varies more or less in size and appearance in different classes 

 of animals, but which has always the same essential characters, and 

 is produced in the same way. 



The egg thus grows in the interior of the ovarian sac, like a tooth in 

 its follicle ; and forms, accordingly, a constituent part of the body of 

 the female. It is destined to be subsequently separated from its at- 

 tachments, and thrown off ; but until that time, it is one of the elements 

 of the tissue of the ovary, and is nourished like any other portion of the 

 female organism. 



Since the ovaries are the. organs directly concerned in the production 

 of the egg, they form the most essential part of the female generative 

 apparatus. Beside them, there are usually present certain other organs, 

 which play a secondary part in the process of generation. The most 

 important of these accessory organs are two symmetrical tubes, or 

 oviducts, destined to receive the eggs at their inner extremity and con- 

 vey them to the external generative orifice. The mucous membrane 

 lining the oviducts is also adapted by its structure to supply certain 

 secretions during the passage of the egg, 

 which are requisite, either to complete it 

 formation, or to provide for the nutrition 

 of the embryo. 



In the frog, the oviduct commences at 

 the upper part of the abdomen, by a rather 

 wide orifice, communicating directly with 

 the peritoneal cavity. It soon afterward 

 contracts to a narrow tube, and pursues a 

 zigzag course down the side of the abdo- 

 men (Fig. 224), folded upon itself in nume- 

 rous convolutions, until it opens, near its 

 fellow of the opposite side, into the " clo- 

 aca" or lower part of the intestinal canal. 

 The oviducts present the general charac- 

 ters described above in nearly all species 

 of reptiles and birds. 



The ovaries, as well as the eggs which 



they contain, undergo at particular sea- 



FEMALE GENERATIVE OR- 



sons a periodical development or increase GA NS OF FRoo.-a, a Ovaries. 

 in growth. In the female fros, during the 6 b Oviducts, c, c. Their internal 



orifices, d. Cloaca, showing inle- 



latter part of summer or the fall, the ova- r i 0r orifices of oviducts. 



Fig. 224. 



Regner de Graaf, Opera Omnia. Arastelaedami, 1705, p. 228. 



