546 EGG AND FEMALE ORGANS OF GENERATION. 



eggs are deposited and hatched in the water, as well as those in 

 which they are retained in the body of the female until the develop- 

 ment of the young is completed, such an egg as above described is 

 sufficient for the formation of the embryo ; since during its develop- 

 ment it can absorb freely, either from the water in which it floats, 

 or from the mucous membrane of the female generative organs, the 

 requisite supply of nutritious fluids. But in birds and in the 

 terrestrial reptiles, such as lizards, tortoises, &c., where the eggs 

 are expelled from the body of the female at an early period, and 

 incubated on land, there is no external source of nutrition, to pro- 

 vide for the support of the young animal during its development. 

 In these instances accordingly the vitellus, or "yolk," as it is called, 

 is of very large size ; and the bulk of the egg is still further in- 

 creased by the addition, within the female generative passages, of 

 layers of albumen and various external fibrous and calcareous 

 envelopes. The essential constituents of the egg, however, still 

 remain the same in character, and the process of embryonic deve- 

 lopment follows the same general laws as in other cases. 



The eggs are produced in the interior of certain organs, situated 

 in the abdominal cavity, called the ovaries. These organs consist 

 of a number of globular sacs, or follicles, known as the " Graafian 

 follicles," each one of which contains a single egg. The follicles 

 are connected with each other by a quantity of vascular areolar 

 tissue, which binds them together into a well-defined and consistent 

 mass, covered upon its exterior by a layer of peritoneum. The 

 egg has sometimes been spoken of as a " product," or even as a 

 " secretion" of the ovary. Nothing can be more inappropriate, 

 however, than to compare the egg with a secretion, or to regard the 

 ovary as in any respect resembling a glandular organ. The egg is 

 simply an organized body, growing in the ovary like a tooth in its 

 follicle, and forming a constituent part of the body of the female. 

 It is destined to be finally separated from its attachments and 

 thrown off; but until that time, it is, properly speaking, a part of 

 the ovarian texture, and is nourished like any other portion of the 

 female organism. 



The ovaries, accordingly, since they are directly concerned in 

 the production of the eggs, are to be regarded as the essential 

 parts of the female generative apparatus. Beside them, however, 

 there are usually present certain other organs, which play a secon- 

 dary or accessory part in the process of generation. The most 

 important of these accessory organs are two symmetrical tube?, or 



