Human Physiology. 249 



proper nest, and hatched either by solar heat or the warmth 

 of one or both of the parents. Animals so born are called 

 oviparous born from eggs. A few fishes, as the shark and 

 skate, lay fecundated eggs like birds, with curiously formed 

 horny shells, and cables for mooring. 



With the mammalia, the higher orders of animals, including 

 the human species, there is still another process. The egg or 

 germ is formed in the ovary of the female. When fully formed 

 it bursts from its containing membranes, with a certain degree 

 of excitement of the generative system, and passes through 

 tubes provided for that purpose into a receptacle called the 

 uterus, or womb. If here met by the seminal fluid, or ferti- 

 lising masculine element, iecundation takes place, a perfect 

 germ is produced, foetal life begins, and the animal is, so to 

 speak, hatched in the womb of its mother, nourished by her 

 blood, and grows until it is ready to come into the world and 

 live its independent life. Animals so produced are called vivi- 

 parous, or born alive. 



The young of the kangaroo, and other marsupials, are born 

 in a very immature condition, and carried in a kind of bag 

 formed upon the abdomen of the mother; within which are 

 the teats from which the little ones draw their nourishment. 



The eggs of birds, from those of the humming-bird, like peas, 

 to the great eggs of the ostrich, which will furnish a dinner foi 

 six men, contain not only the germ, which is very minute, but 

 its supply of food the materials from which its body, bones, 

 feathers, &c., are formed, during the process of incubation or 

 hatching. The white of the egg, almost pure albumen, is not 

 essential to it, but useful as food. The eggs of many animals 

 are without it. The yolk, consisting of albumen and oil, con- 

 tains the matter first taken into the organisation. The germinal 

 spot, a point of matter, is the real germ, and can only be seen 

 under the microscope. The eggs of viviparous animals are of 

 extreme minuteness. That of a dog is the i-i3oth of an inch 



