94 



REPRODUCTION 



about as large as the yolk in an ordinary egg. The larger 

 ones are about ready to escape from the ovary and start 

 to the outside world. When the egg (or yolk) is ready 

 it passes from the ovary into the body cavity and enters 

 the large opening of the oviduct, or egg tube, which 

 carries it to the outside world. As it goes down the 

 oviduct the wall of this tube secretes the albumen (white) 

 all round the yolk. It goes gradually twisting down the 



Figure 23. Diagram of internal anatomy of pigeon. From CoUoti's Des 

 criptive Zoology. 



oviduct and finally comes to rest at a point where the 

 shells are formed around it. Soon afterward the hen lays 

 the egg. 



3. Fertilization and Development. It must be clear 

 that fertilization of an egg like this could not take place 

 as it does in the frog. A sperm could not possibly work 

 its way through the shell or through the sticky albumen. 

 If the egg is to be fertilized, it is necessary for the sperm 

 to unite with it early in its course through the oviduct, 

 and before any of these materials are added. This means 

 that the sperm cells must be inserted in the outer opening 



